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Call No.0^ I H 1*15 Aca&mlfo, 

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Male Figure showing Muscles, from Thomas Geminus* 

Anatomy (1545) after the wood-cut (drawn by John 

Stephen of Galcar?) in Vesalius' De Fabrica (1543) 

(From A. M. Hind Engraving in England in the Sixteenth and Seventeenth Centuries . 
Vol. /, by permission of the Cambridge University Press) 



The Formation 

of the Modern 

Scientific Attitude 


Lecturer in the History of Science, University 
of Cambridge, and Fellow of Christ's College. 











First publistied 1954 



Collegia Christi, suasori meo necnon auctori, 
grato animo 


To the historian of science the University of Cambridge offers 
riches in its manuscripts, its libraries, and its associations. Among 
those who dwell in the places once frequented by Newton, Darwin 
and Rutherford there are many who, quietly and unostentatiously, 
are making their contributions to the understanding of this age 
of science in terms of its long historical evolution. No one who 
has lived with them, no one moreover who has been fortunate 
enough to learn from Charles Raven, Herbert Butterfield, and 
Joseph Needham, can be other than conscious of indebtedness. 

To them, and to all those friends who have helped or tolerated 
my endeavours, I offer my grateful thanks. One other only I 
mention by name, since he is no longer with us, Robert Stewart 
Whipple, whose life-long enthusiasm for the history of science is 
commemorated in the collection of historic scientific instruments 
which he presented to this University. 

Above all, this volume could not have been written without 
the consistent support of my College, which has given generous 
encouragement to the study of the history of science, and the 
interest with which the University has fostered the teaching of 
this subject. 



February 1954 




Chapter I Science in 1500 i 

II New Currents in the Sixteenth Century 34 

III The Attack on Tradition : Mechanics 73 

IV The Attack on Tradition : Astronomy 102 
V Experiment in Biology 129 

VI The Principles of Science in the early Seven- 
teenth Century 159 

VII The Organization of Scientific Inquiry 186 

VIII Technical Factors in the Scientific Revolution 217 

IX The Principate of Newton 244 

X Descriptive Biology and Systematics 275 

XI The Origins of Chemistry 303 

XII Experimental Physics in the Eighteenth 

Century 339 


Appendices : A. Botanical Illustration 369 

B. Comparison of the Ptolemaic and Coperni- 

can Systems 370 

C. Scientific Books before 1500 371 




I HAVE tried in this book to present something in the nature of 
a character-study, rather than a biographical outline, of the 
scientific revolution. Natural science may be defined suffi- 
ciently for my purpose as the conscious, systematic investigation 
of the phenomena revealed in the human environment, and in 
man himself objectively considered. Such investigation always 
assumes that there is in nature a regular consistency, so that 
events are not merely vagarious, and therefore an order or pattern 
also, to which events conform, capable of being apprehended by 
the human mind. But science in this sense is not simply the product 
of one attitude to nature, of one set of methods of inquiry, or of 
the pursuit of one group of aims. Within it there is room for both 
economic and religious motives, for a greater or less exactitude in 
observation (though some measure of systematic and repeated 
observation is essential to science), and for a considerable latitude 
in theorization. 

In many of these respects modern science differs markedly from 
that of a not very remote past. It demands rigorous standards 
in observing and experimenting. By insisting that it deals only 
with material entities in nature, it excludes spirits and occult 
powers from its province. It distinguishes firmly between theories 
confirmed by multiple evidence, tentative hypotheses and un- 
supported speculations. It presents, not a possible or even a 
plausible picture of nature, but one in which all available facts 
are given their logical, orderly places. These are the most impor- 
tant characteristics of modern science, which it acquired during 
the period of transition conveniently known as the scientific 
revolution, and has since retained. Certainly they were long in 
gestation, but it is with the period of their coming to fruition and 
vindication by success that this volume is concerned. Some topics 
I have chosen to omit: mathematics, because it deals not with the 
phenomena of nature, but with numbers; medicine, because it 
was at this time rather an art than a natural science. It has not 



been my object to attempt a complete narration of events, nor to 
dwell on biographical and experimental details. Perhaps these 
omissions may be forgiven in a book designed as an introduction 
to the study of the historical processes at work in the development 
of science, and of the major stages in that development. 

Science began soon after the birth of civilization. Man's attempt 
to win an Empire over Nature (in Francis Bacon's phrase) was 
much older still; he had already learnt to domesticate animals 
and plants, to shape inorganic materials like clay and metals to 
his purposes, and even to mitigate his bodily ailments. We do not 
know how or why he did these things, for his magic and his 
reasoning are equally concealed. Only with the second millen- 
nium B.C. is it possible to discern, dimly, the beginnings of 
science in the coalescence of these three elements in man's 
attitude to Nature empirical practice, magic and rational 

The same three elements continued to exist in science for many 
thousand years, until the scientific revolution took place in the 
sixteenth and seventeenth centuries. Reason, in conjunction with 
observation and experiment, slowly robbed magic of its power, 
and was gradually better able to anticipate and absorb the chance 
discoveries of inventive craftsmen, but complete reliance upon a 
rational scientific method in man's reaction to his natural environ- 
ment is very recent. Magic and esoteric mystery the elements of 
the irrational were not firmly disassociated from serious science 
before the seventeenth century, at which time even greater stress 
than before was being laid on the usefulness to scientists of the 
craftsman's practical skills. This in turn was not outgrown until 
the nineteenth century, when it became clear that in the future 
sheer empiricism and chance would add little to man's natural 
knowledge, or to his natural power. 

Rational science, then, by whose methods alone the phenomena 
of nature may be rightly understood, and by whose application 
alone they may be controlled, is the creation of the seventeenth and 
eighteenth centuries. Since then dramatic achievements in under- 
standing and power have followed successively. In this sense the 
period 1500-1800 was one of preparation, that since 1800 one of 
accomplishment. And it is convenient to conclude this history of 
the scientific revolution with the early years of the nineteenth 


century for other reasons. Though profound changes in scientific 
thought have occurred since that time, and though the growth of 
complexity in both theory and experimental practice has been 
prodigious, the processes, the tactics and the forms by which 
modern science evolves have not changed. However great the 
revision of ideas of matter, time, space and causality enforced 
during the last half-century, it was a revision of the content, not 
the structure of science. In its progress since 1800 the later 
discoveries have always embraced the earlier: Newton was not 
proved wrong by Einstein, nor Lavoisier by Rutherford. The 
formulation of a scientific proposition may be modified, and 
limitations to its applicability recognized, without affecting its 
propriety in the context to which it was originally found appro- 
priate. We do not need sledge-hammers to crack nuts; we do not 
need the Principle of Indeterminacy in calculating the future 
position of the moon: 'the old knowledge, as the very means for 
coming upon the new, must in its old realm be left intact; only 
when we have left that realm can it be transcended.' * 

Despite the progressive accumulation of knowledge and elabora- 
tion of theory, only the broader extrapolations of nineteenth- 
century science would now be described blankly as "wrong," 
though a larger part of its picture of Nature might be described 
as "inadequate" or as "true within certain limits." Even in 
biology, where ancient and extra-scientific notions lingered long, 
where experiment was most tardy in finding its just deployment, 
this is still the case. The systematic and descriptive biology of the 
pre-Darwinian epoch was not rendered futile by the theory of 
evolution. Earlier microscopists were not exposed to ridicule by the 
founders of cytology. On the contrary, the revolution in thought 
about animate nature incorporated, and was founded on, the 
labours of three or four generations. The same could not be said 
of science before 1500, or even, without restriction, of the science 
of the seventeenth and eighteenth centuries. Its progress in these 
earlier times was not by accretion, for it was now and again 
necessary to jettison encumbering endowments from the past. 
Such science was on occasion simply wrong, both in fact and in 
interpretation. Its propositions had to be rejected in toto, not 
merely circumscribed, as the result of experiment and creative 

1 J. Robert Oppenheimer, in his third Reith Lecture (The Listener, vol. L, 
P- 943)- 


thinking. In this respect the beginning of the nineteenth century 
seems a useful point of demarcation between the scientific 
revolution, in the course of which the sciences painfully and in 
succession acquired their cumulative character, and the recent 
period during which that character has been successfully 

The cumulative growth of science, arising from the employment 
of methods of investigation and reasoning which have been 
justified by their fruits and their resistance to the corrosion of 
criticism, cannot be reduced to any single theme. We cannot say 
why men are creative artists, or writers, or scientists; why some 
men can perceive a truth, or a technical trick, which has eluded 
others. From the bewildering variety of experience in its social, 
economic and psychological aspects it is possible to extract only 
a few factors, here and there, which have had a bearing on the 
development of science. At present, at least, we can only describe, 
and begin to analyse, where we should like to understand. The 
difficulty is the greater because the history of science is not, and 
cannot be, a tight unity. The different branches of science are 
themselves unlike in complexity, in techniques, and in their 
philosophy. They are not all affected equally, or at the same time, 
by the same historical factors, whether internal or external. It is 
not even possible to trace the development of a single scientific 
method, some formulation of principles and rules of operating 
which might be imagined as applicable to every scientific inquiry, 
for there is no such thing. Methods of research in each subject 
are too closely bound up with the content and problems of that 
subject for the devising of a mechanical method. 

Nor can we always exploit any dichotomy between the ideas 
and the practice of science, though this dichotomy may be a 
useful tool at times. Interpretations without knowledge and 
knowledge without interpretations are equally unbalanced and 
sterile; any branch of science consists of both. Therefore, since 
knowledge arises from practical operations, the history of science 
can never be a purely intellectual history (like that of mathe- 
matics), nor can it be analysed in a wholly logical manner. For 
ideas arise from facts, and the facts of science may be revealed in 
an order conditioned by chance, by technical resourcefulness, or 
industrial invention. On the other hand, the creative intellect is 
always playing upon the materials provided by techniques of 


experiment, observation or measurement; however subtle these 
become, they can never be said to determine the course of a 
science, unless in a negative sense. 

The dichotomy in science, the fact that its progress requires 
both conceptual imagination and manipulative ingenuity, is 
particularly apparent in the scientific revolution, and presents 
peculiar problems. The reaction against the traditional picture 
of Nature derived from the Greeks occurred simultaneously on 
the factual and the interpretative levels. The theories of the past were 
criticized as being inconsistent, speculative, incomprehensible, 
and as involving spiritual qualities rather than the properties of 
matter; the facts related in the past were challenged as ill-tested, 
spurious, superstitious, and as casually chosen without care in 
observation and experiment. The development of each of these 
phases of criticism may be traced in the later middle ages, when, 
however, they were rarely associated. Even after 1500 many 
exponents of a new attitude failed to perceive that doubts of fact 
and theory were inter-related; that one could not proceed without 
the other. Hence a great part of the force of the "new philosophy" 
of the seventeenth century was due to its dual scepticism, its 
ambition to challenge fact and theory, sometimes without 
consciousness of making a double attack. This duality reinforced 
attention to the question of the logical connection between facts 
and theories, which had also been examined by medieval critics 
of Aristotle. How were the relevant facts to be brought to light? 
How, with the facts known, were appropriate propositions 
concerning them to be arrived at? How could scientific proposi- 
tions be tested by their usefulness in dealing with facts? The early 
success of the scientific revolution owed much to the answering 
of such questions (pragmatically, rather than philosophically) in 
the scientific method combining observation, hypothesis, experi- 
ment and mathematical analysis, a method which demonstrates 
in itself the essential liaison between the factual and interpretative 
levels of inquiry. 

If the scientific revolution cannot be completely depicted, 
even in its origins, as an intellectual revolt against the traditional 
interpretation of Nature, nevertheless such a revolt demands 
primacy of place in tracing its antecedents. Few men have, or had, 
the sense of supremacy of pure fact demanded by Francis Bacon. 
The majority of scientists at all times have sought for facts with 


an object in view. Consequently, the scientific empiricists of the 
seventeenth century, including Bacon himself, pointed to the 
insufficiency of contemporary science before they clamoured for 
more facts on which to frame a sounder doctrine. They did not 
need these facts to teach them Aristotle's mistakes, for of those 
they were already aware; they needed observations and experi- 
ments to avoid falling into fresh errors of their own. Cartesians, 
too, were as confident that conventional science was untrust- 
worthy: because it ignored the method of reasoning from in- 
dubitable truths, and was therefore philosophically unsubstantial. 
And does not Galileo himself refute Aristotle with reason, before 
overwhelming him by experiment? Medieval science, and 
especially the Aristotelean doctrines within it, was not so much 
swept away by a hurricane of uncomfortable facts, as brought 
down by its own internal decay. While the mechanics of Greek 
science, the four elements, the bodily humours, the Ptolemaic 
system, still commanded allegiance (though becoming less and 
less relevant to practical affairs) the Hellenistic view of the cosmos 
was becoming increasingly alien to the European mind. From the 
fourteenth to the sixteenth century men might teach and work in 
science as though they were Greeks of antiquity, but they were not 
so in fact, and the community of thought between Europe and 
Hellas grew ever more formal. By 1600 it was almost academic. 
A demonstration in Greek mathematics or a particular piece of 
reasoning could fire admiration, but the universe could be seen 
through Aristotle's eyes no more. Even his expositors had trans- 
formed him. 

In part this was brought about by the rival Christian authority. 
No Christian could ultimately escape the implications of the fact 
that Aristotle's cosmos knew no Jehovah. Christianity taught 
him to see it as a divine artifact, rather than as a self-contained 
organism. The universe was subject to God's laws; its regularities 
and harmonies were divinely planned, its uniformity was a result 
of providential design. The ultimate mystery resided in God rather 
than in Nature, which could thus, by successive steps, be seen not 
as a self-sufficient Whole, but as a divinely organized machine in 
which was transacted the unique drama of the Fall and Redemp- 
tion. If an omnipresent God was all spirit, it was the more easy 
to think of the physical universe as all matter; the intelligences, 
spirits and Forms of Aristotle were first debased, and then 


abandoned as unnecessary in a universe which contained nothing 
but God, human souls and matter. 

Christianity furnished the scientist with God as the First Cause 
of things. But if this First Cause had, so to speak, set the universe 
to run its course and endowed man with free-will to make his 
own destiny, the phenomena of nature could only be the result of 
determined processes, manifestations of a mechanistic design, like 
an infinitely complex automaton or clock. A clock is not explained 
by saying that the hands have a natural desire to turn, or that the 
bell has a natural appetite for striking the hours, but by tracing 
its movements to the interconnections of its parts, and so to the 
driving force, the weight. If God was the driving force in the 
universe, were not its motions and other properties also to be 
ascribed to the interconnections of its parts? The question, slowly 
compelling attention over three hundred years, received a positive 
answer in the seventeenth century. The only sort of explanation 
science could give must be in terms of descriptions of processes, 
mechanisms, interconnections of parts. Greek animism was dead. 
Appetites, natural tendencies, sympathies, attractions, were mori- 
bund concepts in science, too. The universe of classical physics, 
in which the only realities were matter and motion, could begin to 
take shape. 


EUROPEAN civilization at the beginning of the sixteenth century 
was isolated as it had not been since the first revival of learn- 
ing some four hundred years earlier. Political changes had 
severed traditional links between east and west. The heart of the 
great area of Islamic culture, from which medieval scholarship 
and science had drawn their inspiration, had been over-run by 
the Turks; the eastern Christian centre of Byzantium, the last 
direct heir of ancient Greece, was destroyed; the learned Moors 
and Jews of Spain were expelled by the armies of Castille and 
Aragon. The overland route to China, by which many important 
inventions had been transmitted to Europe, among them the 
new instruments of learning, paper and printing, and over which 
Marco Polo had passed, was now barred. Against this loss of a 
relatively free interchange of ideas and commodities through the 
Mediterranean may be set a developing commercial and scientific 
interest in the promise of geographical exploration across the 
oceans. The Portuguese had brought spices from the Indies; 
Spain had drawn her first golden tribute from Hispaniola. But 
the results of the re-orientation of communications southwards 
and westwards upon the Atlantic had not yet been assimilated, 
and though Europeans were quick to recognize the value of 
negroes or American Indians as slaves, they had not yet learnt to 
appreciate the magnitude of the civilizations in India and China 
with which, for the first time, they came into direct contact. 

Fortunately, when these events occurred, European scholars 
had already emerged from their tutelage, and Latin literature, 
having been enriched with almost everything that Arabic was to 
convey to it, had become creative in its own right. The final 
dissolution of the Christian empire in the Near East, indeed, 
brought to Europe a direct knowledge of classical science with 
which it had been less perfectly acquainted through the Islamic 
intermediary. At the moment when their intellectual communion 
with other peoples was most sharply denied by circumstance, the 


humanistic scholars of the renaissance were most engrossed in 
studying the pure origins of western civilization in Greece and 
Rome. During the next centuries the trend of the middle ages was 
to be reversed; Europeans were to teach the East far more than 
they learned from it. 

In 1500 the fruitful cultivation of science was limited to western 
Europe, to a small region of the whole civilized world stretching 
from Salamanca to Cracow, from Naples to Edinburgh. Even the 
peripheries of this region were illuminated rather by the reflected 
brilliance of the Italian renaissance, than by any great achieve- 
ments of their own. The northern shift of the focus of learning was 
beginning northern Italy had replaced the south and Sicily as the 
cultural centre of Europe but the sixteenth is unquestionably the 
Italian century in science. Scholars, mathematicians, physicians 
everywhere measured their own attainments by Italian standards; 
the Italian universities, and the Italian printing-houses, possessed 
an acknowledged pre-eminence. Beneath inevitable gradations in 
civilization (no less marked in science than in fine art) lay an 
essential cultural unity, undisturbed by nationalism or religious 
schism. Europe had a common tradition; in matters temporal it 
was consciously the heir of Greece and Rome, shaping the texture 
and manner of its own life to the model of their golden age; in 
matters spiritual a single compass of belief had passed from the 
great Councils of the Church through the early Fathers to the 
Papacy and the medieval Doctors. If the secular Empire had 
become a shadow, the spiritual power of the Church seemed still 
firmly founded upon a single theology and a universal orthodoxy 
which had triumphed over Albigenses, Wyclif and Hus. Upon 
this unified Church all learning was in varying degrees depen- 
dent; the universities, themselves papal creations, were religious 
institutions. The study of medicine was the only discipline able to 
stand, to some extent, detached from learning's prime duty to 
theology, and even the teaching and practice of medicine were 
subject to a measure of ecclesiastical control. Human dissection, 
for instance, was strictly supervised by the Church. Learning had 
in Latin its own universal language. The system and content of 
education in every school and university were so similar that a 
scholar could find himself at home anywhere. In each the student 
laboured upon the same texts, graduated by debating similar 
philosophical themes, and (if he progressed as a man of learning) 

SCIENCE IN 1500 3 

found the stimulus to original thinking in problems familiar to all 
men of education. 

It would be mistaken to suppose that, because the intellectual 
life of all Europe at the beginning of the sixteenth century was as 
homogeneous as that of the modern nation state, it was character- 
ized by a dull uniformity. There were, and there had long been, 
distinct and to some extent rival schools, just as there was also a 
special development of some type of study at a particular place, 
theology at Paris, law and medicine at Bologna and Padua. In 
one place men still clung to the pure Aristotelean tradition, at 
another they had begun to criticize it; here the Arabic physicians 
were more highly regarded than the newer Greek texts, there they 
were despised as poisoning the Galenic well of knowledge. Within 
the acceptance of a common body of premisses there was vast 
uncertainty concerning the way in which the premisses should 
be applied. No one doubted that blood-letting was an essential 
part of therapy: but there was great dispute over the actual tech- 
nique. No one doubted that the world was round: but different 
navigators could not agree on the best way to plot a course. No 
one doubted that the calendar was out of joint: but the best 
astronomers could not join in declaring the remedy. It is indeed 
a misleading view of the early stages of the scientific revolution 
to see them as involving only the conflict of two types of premiss, 
as typically in the antithesis between the Ptolemaic and the 
Copernican world-systems. In fact much more was involved, the 
practical and successful handling of detailed problems. This is 
perhaps most clearly seen in the non-physical sciences, in anatomy 
or natural history in the sixteenth century, but it can also be seen 
in the practical arts which depended upon the physical sciences. 
Ultimately, of course, such an art (or science) as navigation 
advanced very considerably through the substitution of the 
Gopernican for the Ptolemaic astronomy; but in the sixteenth 
century greater accuracy in cartography and oceanic navigation 
was independent of the high truths of cosmology. 

The unity of learning which the sixteenth century inherited 
from the middle ages is a strong mark of its diffusion. Scientific 
knowledge in particular showed little differentiation in pattern, 
though it varied greatly in quality and method, because it was 
not the native product of Christian civilization in Europe, 
but imposed upon it. The primitive Germanic tribes had long 


submitted to a Romano-Hellenistic culture: first through their 
contact with the Roman Empire, then through their conversion 
to Christianity and the various efforts towards a renaissance of 
learning that had followed; partly assimilated and legitimized 
(as in witchcraft or folk-medicine), their original attitude to 
Nature had largely sunk to the level of superstition in comparison 
with the "literary" science which won its supremacy in the 
thirteenth century. As a first approximation, it may be said that 
the cultural history of Europe, since the hegemony of the Roman 
city-state, is mainly concerned with the diffusion of Hellenistic 
influences, Greece itself being the heir to the ancient civilizations 
of the Near East. Perhaps the nadir (by either political, economic 
or intellectual standards) was reached about the sixth century; 
by the ninth efforts were being made to assimilate the flotsam 
surviving from the wreck of Roman Imperialism. Islam, em- 
bracing many linguistic and ethnic elements, and having its 
cultural focus in the eastern portion of the former Roman Empire 
which had been less devastated by popular movements than the 
West, possessed greater potentialities for immediate development. 
The Arabic treatise on the astrolabe which Chaucer translated into 
English c. 1390 had been written in the late eighth century; of the 
Islamic medical authorities whom he mentions in the Prologue to 
the Canterbury Tales, two had lived some four centuries before. In 
the first phase of learning among Franks, Saxons and Lombards, 
science had been meagrely represented by a few Latin texts 
fragments of Plato (the Timteus), of Macrobius, and Pliny and 
the degeneration of form and thought from these originals was 
rapid. In the second phase, beginning early in the twelfth century, 
diffusion was concentrated into a very few channels, for the new 
philosophical and scientific literature in Latin was created by its 
very few scholars who were able to translate from Arabic, Hebrew, 
or more rarely directly from the Greek. The most famous of them, 
Gerard of Cremona (c. 1114-87) is credited with making at least 
seventy translations, some of them like Avicenna's Canon, or 
encyclopaedia, of medicine, of vast extent. Though the lists 
certainly exaggerate the personal influence of one individual 
upon the Latin corpus, it cannot be doubted that the somewhat 
arbitrary selection exercised by a small group of linguists had a 
determining effect upon the nature of the material available to the 
purely Latin scholars of later generations. And it must be further 

SCIENCE IN 1500 5 

remembered that the Islamic and Hebrew scientific writings, 
upon which the Latin translators worked, themselves represented 
a fraction accidentally or consciously chosen from the whole 
original literature. 

The intellectual life of medieval Europe was rapidly transformed 
by this acquisition of a sophisticated method and doctrine in both 
philosophy and science. Its influence can be traced in such varied 
directions as the use of siege-engines in war, or the theory of 
government, as well as in astronomy and physics. At first there 
was opposition to the new type of study: the sources, being infidel, 
were suspect, and they seemed to encourage a too presumptuous 
inquiry into matters beyond human comprehension. But the 
simplest Christian attitude, that men should not meditate upon 
this world but the next, and that religion, rather than the works 
of pagan philosophers, should instil the principles of morality 
and ethics, had lost its force. The condemnation of the teaching 
of Aristotle's natural philosophy by a provincial council held at 
Paris in 1210 proved ephemeral, as did later attempts to limit the 
influence of Arabist sources. 1 Even before scholasticism developed 
the study of Hellenistic philosophy upon Christian principles the 
European mind was awake to the value of the riches laid before 
it when refined from theological falsities. Robert Grosseteste 
of Oxford in the first, and Thomas Aquinas in the second half 
of the thirteenth century were the two foremost exponents of 
Aristoteleanism, which as a method of reasoning and a fabric of 
knowledge was thus reconciled with Catholic theology. Inevitably 
the Hellenistic-Islamic renaissance of the twelfth century emerged 
with an even greater homogeneity from this further process of 
moulding. To the extent that Aristotle was seen through the eyes 
of St. Thomas and his influence was profound for it was he who 
made Aristotle the master of medieval thinking the unity of 
medieval culture was reinforced by the single Thomist tradition. 
Averroism, the extreme rationalist appraisal of Aristotle's thought, 
became heresy. Despite Aquinas' deep study of every aspect of the 
Aristotelean corpus, he utterly failed to understand the true spirit 
and methods of natural science, 'and no scientific contribution 

1 George Sarton: Introduction to the History of Science (Baltimore, 1927-48), 
vol. II, p. 568. A reputation for profound acquaintance with Arabic writings 
was, however, long associated in the popular mind with skill in magical arts, 
so that a mass of legend was built up round such a figure as Michael Scot. 


can be credited to him.' 1 Against this dogmatic tradition, the 
exponents of experiment (Grosseteste, Roger Bacon) and the 
mechanistic school of critics (Jordanus Nemorarius, Jean Buridan, 
Nicole Oresme) of the same and later times were generally 
unavailing, though they are interesting and important as the 
precursors of the scientific revolution. 

The time of maturation was really astonishingly short. It is a 
common delusion that medieval intellectual life was stagnant over 
the many centuries that separate the fall of Rome from the rise 
of Florence. On a more just assessment the beginnings of intelligent 
civilization in Europe may be placed no more than four hundred 
years before the Italian renaissance: a longer interval separates 
Einstein from Copernicus, than that which intervenes between 
Copernicus and the earliest introduction of rational astronomy to 
medieval Europe. Within a century of the first translations Latin 
contributions to creative thinking were at least equal to those 
made in any other region of the globe: by the mid-fourteenth 
century the period of assimilation was over, the emphasis lay on 
original development and criticism, and the initiative which it has 
since retained had passed to the West. The renaissance of the 
twelfth and thirteenth centuries was imitative and synthetic; that 
of the fourteenth was exploratory, critical, inquisitive. Authorship 
began to pass from commentary to original composition, although 
still often in the commentatory form. There are signs of true 
science: the development of mathematics, now aided by the 
" Arabic" numerals which were of Indian provenance; anatomical 
research pursued in actual dissection; the development of a new 
mechanics employing non-Aristotelean principles and the rudi- 
ments of a geometrical analysis. At the same time and there may 
be a correlation here which becomes more explicit and conscious 
in the seventeenth century there was considerable technological 
progress. The magnetic compass was first described in Europe by 
Peter the Stranger in 1269; gunpowder was applied to the propul- 
sion of projectiles about 1320; the third of the great medieval 
inventions, printing, began its pre-history about 1400. But these 
are only the most striking examples of a long series: the introduc- 
tion, or wider exploitation of new materials like rag-paper, of 
processes like distillation, of new machines like the windmill or 

1 George Sarton: Introduction to the History of Science (Baltimore, 1927-48), 
vol. II, p. 914. 

SCIENCE IN 1500 7 

the mechanical clock, of new mechanical devices like the stern- 
rudder for ships, or the use of water-power for industrial purposes. 
Although philosophers and theologians still regarded slavery as a 
justifiable social institution, the Latin 1 was the first civilization to 
evolve without dependence upon servile labour. From the eleventh 
century onwards the rigours of villeinage were mitigated and 
servitude disappeared. The phenomenon of the new social fabric 
was, that while the general wealth increased, the inequalities in 
its distribution tended to become more moderate. In fact the 
fourteenth century shows the beginnings of a characteristic of 
modern European civilization, the utilization of natural resources 
through means progressively more complex, efficient and 
economical in the expenditure of human labour. These are the 
first signs of an attitude to Nature, and to technological pro- 
ficiency, which was to become overtly conscious in the writings 
of Francis Bacon but was not to attain its fulfilment before the 
nineteenth century. A manuscript of 1335, written by Guido da 
Vigevano, a court physician who was no insignificant investi- 
gator of human anatomy, already develops the application of 
mechanical skills to the arts of war (in this instance a projected 
crusade to recover the Holy Land) in a manner typical of the 
"practical science" of the Italian renaissance and later ages. 
Again, it must be observed that few of the inventions mentioned 
above originated in the Latin West. The common principles of 
machine-construction were familiar to the later Hellenistic 
mechanicians: other discoveries, like the compass and gunpowder, 
were transmitted to Europe from the Far East through Islam. 
But it was Latin society which was transformed by them, not that 
of Eastern peoples: and it was the Latins who, as in the realm of 
ideas, alone fully realized and extended their possibilities. In the 
end it was the West that rediscovered the East, arriving in the 
ports and coasts of India and China with an admitted technical 
and scientific superiority. 

This is the background to what was once regarded without 
qualification as " The Renaissance." The humanists of the six- 
teenth century, who created the legend of Gothic barbarity, 

1 Since, during the middle ages, not all Europeans were members of the 
Roman Catholic, Latin-writing civilization, it seems convenient to adopt the 
noun "Latins" and the adjective "Latin" in a general sense as descriptive of 
those Europeans who were members of this civilization. 


participated in a new phase of the diffusion of Hellenistic culture. 
For them the past was not merely a store of knowledge to nourish 
the mind, but a model to be directly imitated. Upon them, from 
its newly discovered texts, and from its extant relics in Italy and 
France, the pure light of the Hellenistic world seemed to shine 
directly, and they disdained the reflected splendour of Islam. 
Medieval scholarship seemed limited, obtuse, pedantic. It had 
embroidered and perverted what it had not truly understood. 
Through the perspective of the unhappy and generally, perhaps, 
retrogressive fifteenth century, the whole medieval period was 
seen in a jaundiced aspect. The decay of medieval society, and of 
medieval intellectual traditions, produced a revulsion in the 
minds of the first exponents of an art, literature and science which 
were at once more authentically classical, and more modern. 

The fathers of the Italian renaissance were Petrarch (1304-74) 
and Boccaccio (1313-75); they, with other originators of a new 
literary and artistic movement, were contemporary with the height 
of medieval science. To its exacting discipline and subtle ratio- 
cination the new emphasis on taste, elegance and wit was by no 
means wholly friendly. In one important aspect the renaissance 
was an academic revolt against the tyranny of expositors and 
commentators, but the scholars who turned with renewed 
enthusiasm to original texts came close to surrendering something 
of value, namely the critical analysis and extension of Hellenistic 
science due to generations of Islamic and Latin students of 
philosophy and medicine. These gains, which the superior texts 
of the scholar-scientists of the early sixteenth century would 
hardly have recompensed, would have been sacrificed if the 
renaissance had abandoned the middle ages as completely as the 
academic revolutionaries wished; but such was not the case, and 
to a large extent the fourteenth century was assimilated by the 

As this suggests, there are important reservations to be made 
concerning renaissance humanism as a force making for innova- 
tion in science. For example, it can have had little impact upon 
the early printers who published large numbers of medieval books, 
nor upon the readers who presumably desired them. And in their 
revision of classical authors for the press the scholar-scientists were 
if anything less prone to comment adversely upon them than their 
medieval predecessors. Among the humanists intense admiration 

SCIENCE IN 1500 9 

for the work of antiquity led to the belief that human talent and 
achievement had consistently deteriorated after the golden age of 
Hellenistic civilization; that the upward ascent demanded imita- 
tion of this remote past, rather than an adventure along strange 
paths. Thus the boundary between scholarship and archaism was 
indefinite, and too easily traversecLxSome branches of science 
were indeed directed to new ambitions, others were raised rapidly 
to a new level of knowledge, but it cannot be said that all benefited 
from a single influence favouring realism, or originality of thought, 
or greater scepticism of authority. On the contrary, humanism 
sometimes made it more difficult to enunciate a new idea, or to 
criticize the splendid inheritance from antiquity. Against the free 
range of Leonardo's intellect, or the penetrating accuracy of 
Vesalius' eye, must be set the conviction that Galen could not 
err, or the view of Machiavelli that the art of war would be 
technically advanced by a return to the tactics and, weapons of 
the Roman legion. 

Obviously such rigid adherence to the fruits of humanistic 
scholarship did not yield the renaissance of scientific activity 
beginning in the late fifteenth century. Rather it sprang from the 
fertile conjunction of elements in medieval science with others 
derived from rediscovered antiquity. Softin mathematics the 
revelation of Greek achievements in geometry provoked emula- 
tion, yet the algebraic branch of Islamic origin (for which 
humanism did nothing) made equally rapid progress. Ultimately 
the union of the two effected a profound revolution. Moreover, to 
take a more general point emphasized by Collingwood, 1 the 
renaissance attitude to natural events was so different from that 
of the ancients that the classical revival inevitably led to some 
anomalous results. Thus one may account for the vast interest in 
Lucretius' poetic statement of Greek atomism, De natura rerum, 
rediscovered in 1417, and the eminence granted to Archimedes 
as the archetype of the physical scientist. Already in the fourteenth 
century there were clear signs of an approach to a mechanistic 
philosophy of nature, and the use of mathematical formulations, 
in the physical sciences where such a novel attitude could do much 
to liberate the scientist from discussions of the metaphysics of 
causation and to lead him to concentrate attention upon the 
actual processes of natural phenomena)in this respect the broader 
1 The Idea of Mature (Oxford, 1945). 


interests of humanistic scholarship reinforced a tendency which 
they could not have initiated, a reaction against Aristotle. Although 
the revival of Greek atomism had an important influence, the 
"mechanical philosophy" of the seventeenth century represented 
much more than just this. 

A more complete access to the works of Euclid, Archimedes 
and Hero of Alexandria (among many others) gave a fertilizing 
inspiration to physics and mathematics, but it was on the biological 
sciences that the superior information of the ancients, resulting 
from a more serious attention to observation, had its greatest 
effect. Encyclopaedic study by medical men of the complete works 
of Hippocrates and Galen, by naturalists of those of Aristotle, 
Dioscorides and Theophrastus, played a large part in the scientific 
endeavour of the sixteenth century, only slowly overshadowed by 
original investigation. Even at the close of the century studies in 
the structure, reproduction and classification of plants and 
animals had barely surpassed the level attained by Aristotle. 
Later still William Harvey could regard him as a principal 
authority on embryological problems. Undoubtedly a return to 
purer and more numerous sources of Greek science was a refresh- 
ment and stimulus; despite the imperfections in the renaissance 
scholar's appreciation of the immediate and the remote past, he 
rightly felt that such sources laid before him new speculations, 
facts and methods of procedure, suggested many long-forgotten 
types of inquiry, and disclosed a wider horizon than that known 
to the medieval philosopher. To a growing catholicity of interest 
printing added the diffusion of knowledge. The tyranny of major 
authorities inherent in small libraries was broken for the scholar 
who could indulge in an ease of compilation and cross-reference 
formerly unthinkable. But it is not to be supposed that the method 
of science, or the realization of the problems it was first to solve 
successfully, were simply fruits of the renaissance intellect. Nascent 
modern science was more than ancient science revived. Through 
the revived Hellenistic influence in the sixteenth century, always 
diverting and sometimes dominating the development of scientific 
activity, the strong current of tradition from the middle ages is 
always to be discerned. 

In 1500, when Leonardo da Vinci was somewhat past his prime, 
the scientific renaissance had hardly begun. Scientific humanism, 

SCIENCE IN 1500 ii 

the great critical editions, and the first synthetic achievements 
under the new influences, were the work of the next generation. 
It was once usual to see such men as Nicholas of Cusa, Peurbach, 
and Regiomontanus in the fifteenth century as forerunners of a 
scientific revival, but more recent estimates of their works serve 
rather to emphasize the continuity of thought, than to indicate 
an incipient break jvith the past. And though a vast volume of 
medieval manuscript was left undisturbed and rapidly forgotten, 
the larger proportion of the scientific books printed before 1500 
contained material which was familiar two centuries earlier .(The 
general stock of knowledge had hardly changed, as can be seen 
from such a compilation as the Margarita Philosophica of Gregorius 
Reisch (d. 1525), published in I5O3. 1 This was an attempt at an 
encyclopaedic survey, perhaps rather conservative, certainly 
immensely simplifying the best knowledge of the age, but useful 
as a conspectus of scientific knowledge at the opening of the 
sixteenth century. The pearls of philosophy are divided under nine 
heads which treat of Grammar, Logic, Rhetoric, Arithmetic, 
Music (theoretical, i.e. acoustics, and practical), Geometry (pure 
and applied), Astronomy and Astrology, Natural Philosophy 
(mechanics, physics, chemistry, biology, medicine, etc.), and 
Moral Philosophy. There is also (in the later editions) a Mathe- 
matical Appendix which deals with applied geometry and the 
use of such instruments as the astrolabe and torquetum on which 
medieval astronomy was founded. Reisch's design thus corre- 
sponds closely to that of the typical arts course in the universities 
of the period, which proceeded from the trivium (grammar, 
rhetoric and logic) to the quadrivium (arithmetic, geometry, 
astronomy and music). 

Astronomy was the most systematic of the sciences. The 
phenomena of the heavens had long been subjected to mathe- 
matical operations, though opinions differed on the most suitable 
manner of applying them, and prediction of the future positions 
of sun, moon and planets, the groundwork of astrology, was 
possible to a limited degree of accuracy. Mathematical astronomy 
had been advanced to an elaborate level by the Greeks, and still 
further perfected by the mathematicians of Islam, who had also 
been patient and accurate observers^ Far cosmology in the modern 


1 At least nine editions were printed before 1550; others appeared as late as 
1583 (Basel) and 1599-1600 (Venice). 


sense there was almost no necessity: the universe had been created 
at a determined date in the past in the manner described in Holy 
Writ, and would cease at an undetermined but prophesied date 
in the future. It could be proved, both by reason and by divine 
authority, to be finite and immutable, save for the one speck at 
the centre which was earth, unique, inconstant, alone capable of 
the recurring cycle of growth and decay. As Man was the climax 
of creation, so also the earth (though the most insignificant part 
of the whole in size) was the climax of the universe, the hub about 
which all turned, and the reason for its existence. It was natural 
for men who were unhesitant teleologists to believe that the 
pattern of events was designed to suit their needs, to apportion 
light and darkness, to mark the seasons, to give warning of God's 
displeasure with his frail creation. In varying degrees of sophisti- 
cation such an attitude is universal and primitive, and there may 
be added to it that stage of astronomy, arising immensely later 
in the history of civilization, when the alternations of the skies 
are seen to be cyclic, and therefore calculable. But in the tradition 
of astronomy which prevailed in 1 500 there was a third element, 
of purely Greek origin, which provided a physical doctrine 
describing the nature of the mechanism bringing about the 
appearances. The simple form of this mechanism to which the 
Greeks were led by their reflection on the Babylonian knowledge 
of the celestial motions was described by Aristotle; the complex 
form, capable of accounting for more involved planetary motions, 
was due to Ptolemy. The former was a physical rather than a 
mathematical doctrine, the latter was mathematical rather than 
physical, corresponding to what would now be described as a 
scientific model of actuality. 

In a debased form, and strongly influenced by Platonic 
hylozoism, the simpler Greek theory had never been entirely lost 
to the middle ages. The translators brought Ptolemy's Almagest 
and many Arabic astronomical texts to Latin science. An abstract 
of spherical astronomy, which did not treat of the planetary 
motions in detail, the Sphere of John of Holywood, became a 
common text in the later middle ages and was printed thirty 
times before 1500. The Margarita Philosophica describes the 
"mechanism of the world" as consisting of eleven concentric 
spheres; progressing outwards from the sublunary region with the 
earth as the centre, they are those of the moon, Mercury, Venus, 

SCIENCE IN 1500 13 

the sun, Mars, Jupiter, Saturn, the Firmament (Fixed Stars), 
the Crystalline Heaven, the Primum Mobile, and the Empyraean 
Heaven, "the abode of God and all the Elect." The spheres were 
conceived as of equal thickness, and fitting together without 
vacuities, so that for example the sphere of Saturn was im- 
mediately adjacent to that of the fixed stars. Philosophers were 
less clear on the physical matter of the spheres (Aristotle's perfect 
quintessence as contrasted with the four mutable elements of the 
sublunary world) apart from the fact that they were rigid and 
transparent; having no dynamical theory they were not puzzled 
by problems of friction, mass and inertia. The tenth sphere, the 
Primum Mobile, which imparted motion to the whole system, 
revolved from east to west in exactly twenty-four hours. The 
eighth, bearing the fixed stars, had a slightly smaller velocity, 
sufficient to account for the observed precession of the equinoxes. 
Between these the crystalline heaven was added to account for a 
supposed variation in the rate of this precession. Then, descending 
towards the centre, as the spheres became slightly less perfect, 
more sluggish and inert, each completed its revolution in a 
slightly longer period, so that the sun required 24 hours 4 minutes 
between two successive crossings of the meridian, and the moon 
24 hours 50 minutes, approximately. This increasing retardation 
resulted (as we now know) from a combination of the orbital 
velocity of the earth and the orbital velocity of the planet; the 
whole heavens revolved round the earth once in 24 hours, but the 
sun, moon and planets appeared to move also in the opposite 
direction at much smaller, and varying, velocities. 

With these motions established, simple spherical astronomy was 
taught just as it is today. But this simple theory did not allow of 
prediction, it did not take into account the motion of the moon's 
nodes, causing the cycle of eclipses, nor the variations in brightness 
(i.e. distance) and velocity of the heavenly bodies. It is possible 
to derive predictions from purely mathematical procedures, as 
the Babylonians did, without making any hypothesis concerning 
the mechanism involved. Till modern times the astronomer had 
nothing to work with other than angles, angular velocities, and 
apparent variations in diameter and brightness. He was unable to 
plot the orbit of a planet in space: the best he could do was to 
fabricate a system which would bring it to the proper point in the 
zodiac at the right time. The Greeks, however, could not renounce 


the system of homocentric spheres altogether, and their geo- 
metrical methods based on the circle (in which, it was assumed, 
motion was most perfect since it was perpetual and uniform) 
facilitated the construction of an analogous, but more complex, 
mechanical model. 1 As an example, the system of spheres whose 
combined motions are responsible for the observed phenomena of 
the planet Saturn is thus described by Reisch. It fills the depth, 
represented by the seventh sphere in the simple theory, between 
the interior surface of the sphere of fixed stars, and the exterior sur- 
face of the sphere of Jupiter, both of which are exactly concentric 

with the earth. Taking a 
section through the Saturn- 
ian spheres in the plane 
of the elliptic, A (Fig. i) is 
the outer surface of the 
largest sphere, concentric 
with the earth, B is its interior 
surface which is eccentric. 
C is a wholly eccentric 
sphere, the deferent, carrying 
the epicycle F embedded in 
it. D is the outer surface of 
the third and innermost 
sphere, which is eccentric, 
and E is its inner surface 
which is concentric with the 

FIG. i . The Spheres of Saturn. 

earth. Within E follow the remaining planetary systems of spheres 
in their proper order. The epicycle F, which actually carries the 
planet Saturn, rolls between the concentric surfaces B and D. 

This is the mechanical model, which requires four spheres, 
instead of one, to account for the motions of Saturn. The principles 
of Aristotelean physics were observed, since the spheres by com- 
pletely filling the volume between A and E admit no vacuum. To 
represent the phenomena accurately the astronomer had to assign 
due sizes, and periods of revolution, to the various spheres, which 
were imagined to be perfectly transparent so that their solidity 

1 Both the theories could be represented by actual models. Spherical astro- 
nomy and the doctrine of multiple homocentric spheres was illustrated by the 
Armillary Sphere , of which the Astrolabe is a plane stereographic projection, the 
Ptolemaic theory of planetary motions by the Equatory or computer, which 
seems to be a rather late development in both Islamic and Latin astronomy. 

SCIENCE IN 1500 15 

offered no obstruction to the passage of light to the earth. The 
whole system of Saturn (and of every other planet) participated in 
the daily revolution from east to west; in addition the spheres AB 
and DE revolved in the opposite direction with a velocity of i 14' 
in a century this corresponds to the slow rotation of the peri- 
helion of Saturn's orbit in modern astronomy. The deferent C 
carried round the epicycle in a period of about thirty years, but 
its motion was not uniform with respect to its own centre P, or to 
that of the earth O, but to a 
third point Q so placed that 
OP = PQ, called the equant. 
By this means the unequal 
motion of the planet in its path 
was made to correspond more 
closely with observation. 
Finally, the epicycle itself re- 
volved in a period of one year. 
The great virtue of the epicycle 
which was used by Hippar- 
chus before Ptolemy was that 
it enabled periodic fluctuations 
in the planets' courses through 
the sky, the so-called ' ' stations ' ' 
and "retrogressions" to be 
represented (Fig. 2). 

The epicycle was essentially 
a geometrical device for "saving 
the phenomena," and attempts 
to make a physical reality of it 
were late and unsatisfactory. 
Epicyclic mechanisms similar 
to that of Saturn were required for all the other members of the 
solar system, except the sun itself. Those of Jupiter and Mars were 
identical with that of Saturn, with appropriate changes in the 
values assigned, while the mechanisms for the inferior planets, 
Venus and Mercury, and for the moon, were more complex and 
involved a larger number of spheres. 1 In all, the machina mundi 

1 There is an obvious and necessary relationship between the sizes and speeds 
of rotation assigned by Ptolemy to his circles, and those later adopted in the 
Copernican system, but this relationship is not consistent. With Venus and 


FIG. 2. The Geometry of the Epicycle 
(Jupiter). E, Earth; J, Jupiter. 
The dotted line shows the approxi- 
mate path of the planet, whose 
"stations" occur about B and D, 
and whose "retrogressive" motion 
is from D to B. 



described in the Margarita Philosophica required 34 spheres, but at 
various times much larger numbers had been used in the attempt 
to represent the phenomena more accurately. Once the constants 
of each portion of the mechanism had been determined in accord- 
ance with observation, it was possible to draw up tables from 
which the positions of the heavenly bodies against the background 
of fixed stars in the zodiac could be calculated for any necessary 
length of time. Unfortunately it was well known by 1500 it was 
a scandal to learning that calculations were not verified by 
observation. Eclipses and conjunctions, matters of great astro- 
logical significance, did not occur at the predicted moments. The 
most notorious of astronomical errors was that of the calendar: 
the equinoxes no longer occurred on the traditional days, and the 
failure to celebrate religious festivals on the dates of the events 
commemorated caused great concern. In fact the Julian calendar 
assumed a length for the year (365^ days) which was about eleven 
minutes too long: the necessary correction was adopted in Roman 
Catholic states in 1582. But at the beginning of the century the 
causes of these errors in prediction were by no means clear. The 
current astronomical tables had been computed at the order of 
King Alfonso the Wise of Castille at the end of the thirteenth 
century and were out of date. Were the faults of the tables due to 
the method by which they were prepared based on the Ptole- 
maic system or were they due to the use of faulty observations in 
the first place, the method being sound? The fact that Copernicus 

Mercury Ptolemy's deferent represents the orbit of the earth in the Copernican 
system, and the epicycle that of the planet. With the remaining planets 
Ptolemy's deferent represents the orbit of the planet, and the epicycle that of 
the earth. 

The values of the Ptolemaic constants, and those of their modern equivalents, 
may be compared thus: 

Ratio of Radii Mean Distances 
Epicycle I Deferent (in ast. units) 

Mercury 0-375 : J 
Venus 0-719 : i 


Deferent I Epicycle 

Mars 1*519 
Jupiter 5*218 
Saturn 9*230 


i -ooo 



Angular Velocities 

(deg. per day) 

of Epicycle 

i -60214 
0-98563 [sun] 

of Deferent 
o 52406 

Mean Daily 

i -60213 


o 52403" 
o 08309 


SCIENCE IN 1500 17 

chose the first alternative, that he accepted Ptolemy's observations 
and rejected his mechanical system, was to be of great historical 

It is important to realize and the problems became clearer 
when the first Copernican tables came into use that the diffi- 
culties were not merely conceptual. Suppose that the position of 
Mars is to be predicted within an accuracy of one hour: then the 
position given, and hence the original observations, must be accu- 
rate to less than two minutes of arc, an accuracy quite beyond 
astronomical instruments before the invention of the telescope. A 
large astrolable, of one foot radius, for example, could not usefully 
be divided to less than 5' intervals. For these reasons, certain 
oriental observatories had erected huge gnomon-like instruments 
in masonry to observe the motions of the sun with greater pre- 
cision, and there was a somewhat similar trend towards increase 
in scale in Europe during the fifteenth century. With these it was 
found, however, that as scale increased new errors crept in, and 
the estimated accuracy was not reached. Secondly, mathematical 
procedures were highly involved. In the simplest case it was neces- 
sary to establish (from the tables) the position of perigee in the 
orbit, and then the place of the centre of the epicycle with respect 
to this. Then the rotation of the epicycle itself had to be taken into 
account, and referred to the equant. Finally the position as seen 
from the equant point had to be recalculated as a position seen 
from the earth. Real skill was required to compute a planetary 
position with any accuracy from the tables, and very few even 
in the sixteenth century could confidently undertake the task of 
computing the tables themselves. 

The earth, considering the relative potentialities of human 
knowledge, was much less known than the skies, where the fixed 
stars had already been plotted more accurately than any European 
coastline. It was essential in the prevailing fabric of knowledge 
that the mutable globe and the unchanging heaven be entirely 
distinct. It was unthinkable that the same concepts of matter and 
motion should be transferred from the sublunary to the celestial 
region, and therefore all transient phenomena comets, shooting 
stars and new stars were regarded as mere disturbances in the 
upper region between the earth and the moon's sphere. This was, 
indeed, the region of the element Jire; below it the element air 
formed a relative shallow layer above the surface of the globe. The 


earth was composed predominantly of the remaining two ele- 
ments, water and earth, but with air and fire as it were trapped in it, 
so that when an opportunity for their release occurred they natur- 
ally ascended upwards to their proper regions. Conversely, heavy 
substances made largely of earth and water sought to descend as 
far as possible towards the centre of the cosmos, where alone they 
belonged, the water lying upon the earth. It was believed before 
the age of geographical discovery that only a sort of imbalance 
in the globe enabled a land-mass fit for human habitation to 
emerge in the northern hemisphere. 

The categories of motion played an extremely important part 
in pre-Newtonian science: even Galileo did not succeed in liber- 
ating himself from them completely. Perfect circular motion was 
an unquestioned cosmological principle, which gave consistency to 
the whole theory of astronomy. In the sublunary region natural 
motion was invariably rectilinear: away from the earth's centre 
in the case of the light elements, and towards it in the case of the 
heavy. Since the centre of the earth was a fixed point of reference 
the definition of these species of motion occasioned no philo- 
sophical difficulties. The earth and its elements were unique, and 
as a concept like " heaviness," having no relation to anything but 
the sublunary region (to apply it elsewhere would be meaningless) 
could only refer to a body's tendency to move away from or 
towards the centre of the earth, so also definitions like "up" and 
"down" could be quite unambiguous. Violent motion on the 
other hand, that is raising that which is naturally heavy, or 
lowering that which is naturally light, was unprivileged and could 
occur in any direction. Force was required to effect these violent 
movements, because they were opposed to the natural order of 
the universe, just as force was required to withdraw a piston from 
a closed cylinder because nature abhors a vacuum. As soon as 
the effective or retaining force ceased, natural motions would 
restore the status quo ante. This plausible, though limited, doctrine 
was of great importance as the foundation of mechanics. Man was 
the agent of the great number of violent motions, and one reason 
why mechanics played a minor role in the tradition of science until 
the sixteenth century was perhaps just this fact that so much 
mechanical ingenuity was directed towards reversing the natural 
order it did not contribute to the understanding of nature, but 
violated it. 

SCIENCE IN 1500 19 

A corollary drawn from the classification of motion again 
distinguished celestial from terrestrial science. Motion was the 
ordinary state in the former, rest natural in the latter. Wherever 
the notion of inertia has been perceived, however dimly, it has 
been seen most clearly exemplified in the motions of the 
heavenly bodies. While natural motion in the sublunary region 
exists for Aristotle as a possibility, it is clearly exceptional, except 
in connection with the displacements effected by living agents. 
In terrestrial mechanics, therefore, attention was most obviously 
drawn to the compulsive or violent motions brought about by the 
action of a force, and the natural motions which follow afterwards 
in reaction, e.g. the fall of a projectile. It was not difficult, once 
the question of mechanics was approached in this way, to conceive 
of force as producing motion from the state of rest, and as the 
invariable concomitant of violent motion. Within itself inert 
matter could have no potentiality for any other than its proper 
natural movement: and though Aristotle never explicitly formu- 
lates the proposition that the application of a constant force gives a 
body a constant velocity, it is implied in the whole of pre-Galilean 
mechanics. The natural order could not be defied save at the cost 
of expending some effort, any more than a weight could be 
suspended without straining the rope by which it is hung. As 
against this simple principle there was a whole category of 
phenomena of motion that had to be treated as a special case, of 
which the motion of projectiles was the leading instance. 

Observation could not overlook the fact that no form of motion 
ceases instantaneously. Effort is required to stop a boat under 
way, or a rapidly revolved grindstone. What was the source of re- 
sidual force which could impel an arrow for some hundreds of feet 
after it had left its mover, the bow-string? The main Aristotelean 
tradition pronounced that the force resided in the medium, air 
or water, in which the motion took place, the medium being 
as it were charged with a capability to move, though it did not 
move itself. The medium, indeed, plays a most important part in 
the Aristotelean theory of motion, for it is its resistance to move- 
ment which is overcome by the application of a constant force, 
limiting the velocity which can be attained. If a vacuum in nature 
were possible (and this Aristotle denied), a moving body could 
attain an infinite velocity since there would be nothing to limit it. 
In this special case, then, the medium has a dual function: its 


resistance brings the moving body to rest, but its charge of motion 
protracts the movement after the effect of the force has ceased. 
This apparently contradictory dualism was severely criticized by 
philosophers who otherwise worked within the general framework 
of Aristotelean science, and an alternative theory of motion was 
put into a definitive, and to some extent mathematical, form in the 
fourteenth century, principally by two masters of the University 
of Paris, Jean Buridan and Nicole Oresme. The principle they 
adopted, but did not invent, was that though rest is the normal 
state of matter, movement is a possible but unstable state. They 
illustrated this conception by analogy with heat: bodies are usually 
of the same temperature as their neighbourhood, but if they are 
heated above that temperature, the unstable state is only gradually 
corrected. A moving body acquired impetus, as a heated body 
acquired heat, and neither wasted away immediately. The 
impetus acquired was the cause of the residual motion; and only 
when the store was exhausted did the body come to rest. 1 

Although the idea of motion as a quality of matter was retro- 
gressive, and the analogy with heat false, the development of the 
mechanical theory of impetus is of outstanding importance in the 
history of science. Impetus mechanics was not widely diffused, and 
the line of investigators who continued discussion of its tenets 
down to the sixteenth century was somewhat thin. It is not dis- 
cussed in the Margarita Philosophica, but it was well known to 
Leonardo da Vinci, Tartaglia, Cardano and other Italians of the 
renaissance period. In its finished form it is absolutely a medieval 
invention, which was never displaced by the Hellenistic revival. 
The notion of impetus was not inspired by any new observations 
or experiments, nor did it suggest any. The facts which it sought 
to explain were exactly those already accounted for in the original 
Aristotelean theory. But it was the work of truly creative minds. 
Before the idea of impetus could be useful, it enforced a revalua- 
tion of ideas on the nature of motion and, still more important, 
of ideas on the natural order. Ideas of motion, even in Aristotelean 
physics, and still more in that of Plato before him and some 
medieval philosophers later, had been integrally woven into a 

1 Part of the difficulty of the early mechanicians lay in the disentangling of 
such concepts as motion, velocity, inertia, kinetic energy, just as much later 
the physics of heat was obstructed until the concepts of temperature, heat, 
entropy were defined. 

SCIENCE IN 1500 21 

fundamentally animistic philosophy of nature, to the extent that 
in the extremest form motion and change were denied to matter 
except in so far as it was pushed, pulled or altered by various ani- 
mated agencies. The theory of impetus, attributing to inert matter 
an intrinsic power to move, was a decisive step in the direction 
of mechanism. In a sense it first conferred a true physical property 
upon matter, qualifying it as more than mere stuff, the negation of 
empty space. The impetus theory contained the first tentative 
outlines of the explanation of all changes in nature in terms 
solely of matter and motion which was to figure so prominently 
in the scientific philosophy of the seventeenth century. Indeed, 
both Buridan and Oresme foreshadow the greatest triumph of 
seventeenth-century mechanism, Newton's theory of universal 
gravitation. Since the heavenly spheres were perfectly smooth 
and frictionless, moving upon each other without resistance and 
without effort, they saw that when the whole system had been set 
in motion it would revolve as long as God willed, without its 
being required that each sphere should be animated by a guiding 
intelligence. 1 

Although medieval science was ignorant of dynamics in the 
modern sense, discussions of motion and the displacement of 
bodies form a very important element in its physical treatises. 
The other branch of mechanics, statics, although it was of some 
practical usefulness, remained in a very rudimentary condition 
until the rediscovery of Archimedes' work in the sixteenth century. 
His famous hydrostatical principle was known to the middle ages, 
but even such an original and profound writer as Oresme failed 
to apply it successfully as for instance in his explanation of the 
fact that a given piece of wood may weigh more in air than 
another of lead, and yet be lighter than the lead in water. 2 Even 
the theory of the lever and the balance was imperfectly appre- 
hended. In these subjects the classical inheritance was weak; the 
authority followed was Aristotle; and the medieval writers had 
failed to develop an experimental tradition of their own. In optics 
they had a much surer foundation, in the original work of Ptolemy 
and its extension by the Arab Ibn al-Haitham (Latine Alhazen, 

1 A. D. Menut and A. J. Denomy: "Maistre Nicole Oresme, Le Livre du 
Ciel et du Monde," Medieval Studies, vols. Ill, IV, V (1941-3), esp. IV, pp. 181 
et seq. 

2 Ibid., vol. V, pp. 213-14. 



c. 965-1039). Alhazen had actually conducted experiments, and 
made measurements, and in the West the experimental and geo- 
metrical study of optics was continued by such men as Robert 
Grosseteste and Roger Bacon in the thirteenth century. Shortly 
after the latter's death a great advance was made in practical 
optics with the invention of spectacles. The magnification of 
objects by lenses, unrecorded in antiquity, was known to Alhazen; 
their ophthalmic use brought the glass-grinder's craft into being. 
As a result the Margarita Philosophic^ for example, offers a more 

C.H.=Crystfl/f/ne Humour 

FIG. 3. Section through the human eye, from the Margarita 
Philosophica (translated). Nuca perforata = Iris,Secundina 
Choroid, Crystalline Humour = Lens, Spider's Web 
? Ciliary processes. 

rational and complete account of the phenomena of light than of 
any other part of physics though it is to be found under a dis- 
cussion of the powers of the "sensitive soul" not in the section on 
natural philosophy. Light is defined as a quality in the luminous 
body having an intrinsic power of movement to the object, which 
may be either the eye or an opaque body thus illuminated. Colours 
are somewhat similarly described as potential qualities in the 
surfaces of bodies which are made actual by the incidence of light. 
Next the structure of the eye is described, with the aid of a good 
diagram of a section through the organ, and the functions of the 
seven tunics and four humours are explained (Fig. 3). The optic 
nerve is said to conduct the " visual spirit" to the brain, and single 

SCIENCE IN 1500 23 

vision with two eyes is simply accounted for by the union of the 
two optic nerves into a single channel. The shining of rotten fish 
or fireflies is attributed to the element of fire in the composition 
of their substance. 1 Reflection and refraction are quite intelli- 
gently treated. The fact that the ray of light passing from a rare 
medium to a dense (as from air to water) is refracted towards the 
perpendicular is explained by the greater difficulty of penetration. 
Examples of the effects of refraction, such as the apparent bending 
of a stick in water, are elucidated by simple geometrical figures, 
and the apparent enlargement or diminution of the object seen in 
accordance with the size of the visual angle at the eye is described. 
In another section of the book the appearance of the rainbow is 
explained: where tiny drops of water in the clouds are most dense 
the sunlight is reflected as of a purple colour, where they are less 
dense the colour is weaker and the light appears green, the 
blue is the weakest of all. Refraction is not referred to in this 
connection. Acoustics also was comparatively well under- 
stood, both theoretically and experimentally. Reisch described 
the physiology of the ear, the nature of sound as a vibration, and 
the transmission of perception to the brain through the nerves 
by means of an ' 'auditory spirit." Music of course had its own 
peculiar theory and practice, which are carefully outlined in the 

Other aspects of the knowledge of material things, which refer 
rather to their composition, structure and generation than to the 
phenomena which arise from motion of some kind, were broadly 
related to the theory of matter derived from Aristotle. That all 
substance accessible to human experience is composed of the four 
elements, fire, air, water and earth, in varying proportions, seems 
to have been a notion to which the earliest philosophers were 
favourably disposed: it was accepted among the Greeks in pre- 
ference to the single-element theory of Thales, and very similar 
ideas prevailed in China and India. It was not required that every 
analysis should yield these elements in identical form, nor was 
there any means by which such an exact identity could have been 
determined; but it is clear that the three ponderable elements 
correspond roughly to the three states of matter (solid, liquid, 
gaseous), with heat added as a material element. This conception 

1 Phosphorescence was studied with much interest in the later seventeenth 
century, e.g. by Robert Boyle. 


of heat (and electricity) as material though imponderable fluids 
elements in fact if not in name had not become an anachronism 
even by the end of the eighteenth century. A great deal of learning 
was devoted to the question of how mixed bodies are compounded 
from the elements, and how bodies generate by a synthesis of 
elements, or corrupt by their dissolution. An important philo- 
sophic problem was the relationship between the composition of 
a substance and its qualities, or properties. Plato's doctrine of 
"essential forms," or ideal models, exercised its pernicious 
influence indirectly throughout the middle ages. Aristotle and 
his followers believed that the elements themselves could be 
transmuted from one to another, so that water could be condensed 
into earth, or rarefied into air. Again, in a more strictly chemical 
form, this conception lingered to the eighteenth century. The four 
elements were of undefined figure, and matter was thought of as 
being continuous. Ancient atomistic speculation was known to 
the middle ages through Aristotle's criticism of it, but that 
criticism was regarded as wholly convincing. The conjunction of 
elements in a compound body took place without any conceivable 
hiatus or division; as Oresme says, they are not mingled like flour 
and sand, for every fraction of the infinitely divisible compound 
must contain all its elementary constituents. 

Regarding this framework of ideas from the point of view of 
the chemist or mineralogist, its most important feature was the 
latitude it offered for an infinite variety of theorizing on the 
nature of change in substances. The only certain definition of a 
substance was that it must have form (i.e. fill some volume of 
the universe) and substance (i.e. be material), and possess either 
gravity or levity. Form and substance are therefore in one sense 
(as Oresme remarks) the first elements of matter; the four 
elements proper have a secondary role and are transmutable. 
Form likewise is obviously mutable: only substance could remain 
constant, since its destruction or creation would require a change 
in the fixed finite volume of the universe. Consequently, what we 
should now call physical or chemical changes could be accounted 
for on any of three hypotheses: (i) variation in the proportion of 
elements, (2) the generation of elements (fire being the noblest in 
the series), (3) the degeneration of the elements. Ex nihilo nihilfit. 
The first has in fact formed the main subject of chemistry, but 
this limitation was only logically established by Lavoisier. In this 

SCIENCE IN 1500 25 

period the modern distinction between physical and chemical 
changes would have had no meaning, since this differentiation of 
properties was not yet established. The analogy, involved in the 
use of such terms as "generation," between organic and inorganic 
matter was consciously cultivated, being a natural product of the 
animistic conception of nature. As the plant grows from earth and 
water, so equally well could metals, gems and stones. 1 In the 
seventeenth century it was still believed that veins of ore would 
grow in a mine if it was left to rest for a time unworked. And by 
various natural or artificial processes (the calcination of metals, 
the combustion of organic materials) one or more of the con- 
stituents could be recovered. A vital principle, though of a 
humbler kind, was just as much present in the sand which grew 
into a pebble, as in the seed that grew into an oak. Natural history 
has only comparatively recently ceased to signify mineralogy as 
well as biology, and the apprehension of the problems of formation 
and change in the organic world as involving problems of a 
different order from those encountered in the inorganic is a 
comparatively late product of the scientific revolution. In so far 
as it demands a differentiation between organic and inorganic 
chemistry it was never appreciated by Robert Boyle. And it must 
be remembered that while it was possible to cite as examples of 
matter "salt" or "flesh" without any doubt that the two were 
precisely comparable, philosophy imposed an even higher degree 
of theoretical unity. For the elements figuring in chemical change 
were the elements of the sublunary world in cosmological 
theory. The structure of explanation had to be consistent 
between the macrocosm and the microcosm; the properties 
of "fire" or "air" as they were stated in the general picture 
of the universe had to recur precisely when these elements 
were considered as entering into the composition of organic 

Closely allied to the theory of four elements was the doctrine of 
the four primary qualities heat, cold, dryness and humidity. A 
combination of a pair of these qualities was attributed to each ele- 
ment, fire being dry and hot, air hot and moist, water moist and 
cold, earth cold and dry, and from mixtures of these elementary 
qualities the secondary material qualities, hardness, softness, coarse- 
ness, fineness, etc., were in turn derived, though other qualities 
1 But see below, p. 27. 


like colour, taste, smell, were regarded as intangible. 1 Thus the 
transmutation of elements was accomplished by successive stages 
through substitution of qualities: dried water becomes earth, 
heated water becomes air, but to transform water to fire it must 
be both heated and dried. It was reckoned that with each trans- 
formation the volume was multiplied by ten, so that fire had 
i/i,oooth part of the density of earth. Meteorological phenomena, 
for instance, could be accounted for by the application of these 
ideas in detail. The sun's heat turns water into air; the element 
air, being light, rises; but high above earth (where it is cold) air is 
transformed into water, and water being a heavy element falls 
as rain. Similarly air in the caverns and cracks of hills is cooled till 
it becomes water, which runs out as a spring. Comets are a hot, 
fatty exhalation from the earth drawn into the upper air and there 
ignited. The generation of "mixed substances" such as minerals 
and metals in the interior of the earth under the action of celestial 
heat from the primary elements and qualities was considered as a 
more complex example of the same process. Stone is earth coagu- 
lated by moisture. Sal-ammoniac, vitriol and nitre are listed in the 
Margarita Philosophica as examples of salts formed from the coagu- 
lation of vapours in different proportions; to mercury, sulphur, 
orpiment, arsenic etc. a similar origin is attributed. The metals 
were commonly supposed to result directly from a combination 
and decoction of mercury and sulphur though, as the alchemists 
insisted, not the impure, earthy mercury and sulphur extracted 
from mines and used in various chemical processes. Reisch, while 
he admits the theoretical possibility of transmuting metals, points 
out the great difficulty of imitating the natural process of their 
generation precisely, and seems doubtful of the pretensions of the 
alchemists. Indeed, the ambition to tincture the base metals and 
otherwise modify their properties so that they should become in- 
distinguishable from gold is far older than the Greek theory of 
matter which gave it a rationale, and the actual processes or recipes 

1 The medieval theory of matter was derived mainly from Aristotle's 
De Caelo (III, 3-8), De Generations et Corruptione (Bk. II), and Meteorologies 
Cf. De Gen. et Corr. 9 II, 3: * hence it is evident that the "couplings'* of the 
elementary bodies will be four: hot with dry and moist with hot, and again 
cold with dry and cold with moist. And these four couples have attached 
themselves to the apparently "simple" bodies (Fire, Air, Water and Earth) in a 
manner consonant with theory. For Fire is hot and dry, whereas Air is hot and 
moist (Air being a sort of aquaeous vapour) ; and Water is cold and moist, while 
Earth is cold and dry.' 

SCIENCE IN 1500 27 

traditional in the art of alchemy, some of which can be traced to 
pre-Hellenic antiquity, had little reference to the philosophic idea 
of metallic generation. But so long as the organic-inorganic analogy 
seemed plausible, alchemy could not be dismissed as mere folly. 
As for the differentiation between the generation from the 
elements of the world of inorganic substances like minerals, and 
the generation of living organisms, it is obvious that this could 
not be found merely in the principle of growth, or autogenous 
development from a seed, for this was really common to both. It 
could not be made material at all, and therefore the two broad 
kinds of living nature were defined as possessing respectively a 
vegetative and sensitive "Soul," man alone having in addition an 
intellectual soul which gives him the power of reason. In members 
of the vegetative class (plants) the organization of matter was 
more subtle than in minerals: they were not passive creatures of 
nature, like a stone, for they required to be supplied with water 
and rich soil if they were to maintain their existence, they showed 
cyclical variations, and they possessed special structures for repro- 
ducing their own kind. The fixing of the margin of life is not 
simple; our phrase "living rock" is the survival of an ancient 
mode of thought, and the alchemists used to distinguish between 
the "dead" metal extracted from the ore and the "live" metal in 
the veins of the mine. But the need for nourishment, involving 
some process of "digestion," and the possession of a reproductive 
system were recognized as distinctive of living creatures. It was 
certain from theology that these had been created in the beginning, 
and perpetuated themselves without change ever since. The func- 
tion of the vegetative soul was to control and indeed be the bio- 
chemistry of the organism, the whole life of the plant, but only 
a part of the life of the animal. For the animal is sensitive: it feels 
pain, it is capable of movement, it can manifest its needs and 
desires. Therefore it was endowed with a sensitive soul. Man has 
both a vegetative soul, since he must digest and reproduce, and a 
sensitive soul because he possesses a nervous system, and he alone 
being endowed with the power of reflection, of detaching himself 
from the mechanism of the body, was credited with the third, 
intellectual soul. The matter was everywhere the same, in rock, 
in tree, or in dog, for it was well known that certain wells and 
caves had the power of transmuting wood into stone, for instance: 
the distinction between the animal, vegetable and mineral 


kingdoms lay in the immaterial organizing principle which brought 
the elements into conjunction: nature could make pebbles grow 
in streams, but not grass without seeds. 

There was one important exception to this rule, founded (un- 
fortunately) on the authority of Scripture and Aristotle alike. 
A group of organisms, small as Aristotle originally conceived it, 
obviously possessing the characteristics of life, seemed to have no 
special mechanism of generation, but to develop directly from 
decaying matter. Some insects, lichens, mistletoe, maggots were 
included in the class of spontaneously generated creatures which 
had no specific descent, and to them the middle ages, from sheer 
ignorance, added others such as the bee, the scorpion, and even 
the frog. Once spontaneous generation had been admitted, it was 
a fatally easy alternative to investigation, and the belief remained 
unshaken till the mid-seventeenth century. Yet it was less anoma- 
lous than it might seem at first sight, for Aristotle was able to 
imagine the circumstances in which spontaneous generation might 
occur after a fashion that corresponded closely with his ideas on 
normal reproduction. Since the whole universe was in a sense, not 
the full sense, animated, it was not illogical that some humble, 
borderline creatures should be born of it without parents. 

Of the excellent descriptive biology of Aristotle and Theo- 
phrastus very little was known at the opening of the sixteenth 
century. The middle ages had depended only too much on 
compilers of the later Roman period and on fables both pagan and 
Christian. Such study was excluded from natural philosophy; it 
might be just respectable as a form of general knowledge, or 
moral as it provided material to illustrate a sermon or emphasize 
the minuteness of divine providence, but it offered none of the 
sterner food for thought. Botanical or zoological curiosity is of 
very recent origin; in most periods most men have been content 
to acquire only the minimum of practical knowledge. A very 
few in the middle ages, like Albert the Great or the Emperor 
Frederick II, had an interest and attend veness far above the 
ordinary, but they founded no tradition. Observation was blunted, 
and it has been pointed out that naturalistic representation must 
be sought not in learned treatises, but in the works of craftsmen, 
artists, wood-carvers and masons. Botany was cultivated to a 
minor extent as a necessary adjunct to medicine and medieval 
herb-gardens included both edible vegetables and medicinal 

SCIENCE IN 1500 29 

simples. In pharmacology native Germanic lore mingled with 
the remnants of Hellenistic botany, so causing much confusion. 
Plants named and described by the Greeks were identified with 
the different species of western Europe; the nomenclature itself 
varied widely from place to place; and there was no system by 
which one kind could be recognized with certainty from its 
structure and appearance. As the quality of graphic illustration 
and of verbal description deteriorated, the herbal became little 
more than a collection of symbols, so that the mandrake which was 
originally recognizable as a plant becomes a manikin with a tuft 
sprouting from his head. Again, on the purely empirical side, 
some progress was made in the selection of strains of corn, just as 
it is certain that attention was given to the breeding of hawks and 
hounds, but in none of these things was the plant or animal itself 
the centre of interest. It existed simply to be cooked, or distilled, 
or mutilated in man's service, or alternatively to play a part in 
symbolisms of endless variety. There are, however, signs of a 
more naturalistic outlook from the earliest beginnings of the 

Natural history and scientific biology are both modern creations, 
stimulated indeed by the rediscovery of Greek sources in the 
sixteenth century. But this was not the only fruit of the Italian 
renaissance, for naturalism is older in art than in science. It is 
unnecessary here to discuss at length a change in the artist's spirit 
and ambition which had such important consequences for biology 
and medicine. It is at least fairly clear that the medieval draughts- 
man was not simply incapable of attaining realism, e.g. in matters 
of perspective, but was not interested in perfecting direct repre- 
sentation. The element of symbolism was as important to him as 
it has been in the twentieth century. No tradition of " photo- 
graphic realism" existed which could serve the purposes of science, 
such as was assiduously cultivated with the aid of perspective 
instruments, camera lucida, and other devices from the seven- 
teenth century to the perfection of photography, when art and 
science again parted company. Partly under Hellenistic influence, 
partly for internal reasons, art moved strongly in the direction 
of realism and the faithful representation of nature in the fifteenth 
century. Plants and animals became recognizable as individuals 
rather than hieroglyphs. The tradition that artists should study 
the anatomy of the animals and men they depict came into being, 


reaching its peak in Leonardo da Vinci. This development was 
powerfully reinforced in its scientific importance by the invention 
of printing. Biology is peculiarly dependent upon graphic illus- 
tration, and it is essential not merely that the illustration should 
be accurate in the first place, but that it should be capable of being 
reproduced faithfully. Nothing becomes corrupt more easily 
than a picture or diagram repeatedly copied by hand; only a 
mechanical process of reproduction, like the woodcut or the later 
copper-plate, can maintain faithful accuracy. At the moment 
when the technique of visual representation was arousing great 
interest in the draughtsman and artist, printing made it possible 
for illustrations to be copied in large numbers for teaching pur- 
poses, so that the anatomical student and the botanist could 
recognize the form of the organ or plant described in the text 
when he saw it in the natural state. 

The potentialities of the new interests and skills in biology 
began to emerge only in the sixteenth century, as living creatures, 
in their beauty, in the fascination of their habits, in the variety of 
their species and ecological inter-relations, aroused a curiosity 
and sentiment which has grown steadily in its extent throughout 
the modern period. The faithful imitation of nature the necessary 
formal basis of all naturalism was an aesthetic, rather than a 
scientific revolution; the romantic nature-lover may not be a good 
biologist. It was not until thought began to play upon the new 
facts and the faults in the old traditions which passed for natural 
history that precise observation could reveal consequences im- 
portant for science, or that science could see in the flower not 
simply an aesthetically pleasing object, or a symbol of God's 
mysterious and benevolent ways, but a challenge to man's powers 
of understanding. 

Science is an expanding framework of exploration, not the 
cultivation of special techniques, or of a pecularly acute apprecia- 
tion of the wonder and unexpectedness of the universe in which 
we live. Medieval philosophers, who in this respect had a sharp 
sense of reality and a just notion of the importance of intellect, 
had left natural history to such compilers as Bartholomew the 
Englishman (c. 1220-40) whose book is an uncritical compendium 
of classical fable and old wives' tale, flavoured with moralizations 
and somewhat rarely enlivened by a touch of the countryman's 
lore. They judged that the typical was more significant than the 

SCIENCE IN 1500 31 

freak, unlike some of the scientists of the later seventeenth century 
who, in misguided zeal for the principles of Francis Bacon, filled 
the museum of the Royal Society with the heads of one-eyed 
calves, internal calculi, an artificial basilisk. 1 None of the great 
men of the middle ages, with the exception of Albert the Great, 
showed more than a cool interest in natural history. As a result, 
bestiaries, herbals and encyclopaedias were laborious summaries 
of the bald notes available in classical sources, and none of them 
carried more than the slightest indication of personal observation. 
Heraldic beasts were listed with real animals; the legends of the 
crocodile's tears, the pelican killing its brood and reviving them 
with its blood, and the barnacle-goose born of rotten wood added 
interest to the story: the lion and the fox became popular symbols 
of bravery and cunning. Creatures were classified according to 
the element in which they lived. The salamander was the only 
known inhabitant of fire; birds belonged to air; fishes, whales, 
mermaids and hippopotami to water; and the rest to land. Trees 
and herbs formed the two kinds of vegetable life, but only the few 
species useful to man were noticed. Even common garden flowers 
were ignored. Such work of compilation was regarded as a purely 
literary task, and the authorities were quoted in wholly uncritical 
fashion. Some scholars developed fantastic etymologies, such as 
Neckham's Aurifrisius [Osprey] from " Aurum Frigidam sequens." 
Roger Bacon pointed out the difficulty of interpreting satisfactorily 
the more obscure names of creatures mentioned in the Bible 
Biblical exegesis was one of the few respectable motives lor 
studying natural history at all. 2 It scarcely existed save as an 
appendix to some other branch of study. This is not really sur- 
prising, since it is a trait of a sophisticated society to be interested 
in things of apparently no concern to humanity. Natural philo- 
sophy had for the middle ages an established place in the House 
of Wisdom: natural history had yet to establish itself. 3 

Francis Bacon wrote of scholastic philosophy that, from 
immediate perceptions of nature, it 'takes a flight to the most 
general axioms, and from these principles and their truth, settled 
once for all, invents and judges of intermediate axioms. 5 Once 
fundamental doctrines, the immovable earth, the four elements, 

1 Cf. Nehemiah Grew: Musawn Regalis Societatis (London, 1681). 

2 C. E. Raven: English Naturalists from Neckham to Ray (Cambridge, 1947). 
8 Cf. Appendix A. 


or the souls of living organisms, are accepted as unshakably 
true, and explanations of the varied phenomena of nature 
deduced from them, it is an inescapable consequence that the 
structure of scientific knowledge has great cohesion, a logical 
unity imposed from above. An empirical science, a science which 
sees itself as unfinished and progressive, can tolerate inconsisten- 
cies it is for the future to resolve them by some higher-order 
generalization. Physicists might have debated for a hundred 
years whether light is undulatory or corpuscular in nature, but 
the progress of optics did not wait upon a resolution of the argu- 
ment. And while it is far from being true that medieval science 
was exclusively deductive or exclusively speculative in every 
detailed consideration of a particular phenomenon, it is true that 
its structure was of the form that Bacon described. The character 
of the structure is not changed by the fact that some philosophers 
made a few experiments. The structure of modern physics is still 
experimental, though some physicists do not make experiments. 
The difference is that the theoretical physicist bases his calcula- 
tions upon materials obtained by the researches of an experimental 
physicist and produces a result which is itself capable of confir- 
mation by experiment, whereas the medieval philosopher fitted 
the results of his experiments into a theory already firm in his 
mind. He knew what "light" was before making experiments on 
refraction: he knew the cosmological significance of " weight " 
before attempting to determine the speeds at which heavy bodies 
fall. Experiment and induction could only modify the minutiae of 
science, and these (for example, the numerical value of astro- 
nomical constants) were indeed frequently changed in the later 
middle ages in accordance with experience. They could not 
reflect upon the broad lines of the structure. It might indeed have 
happened that Aristotelean science would have been crushed 
under the accumulated weight of an adverse mass of experimental 
testimony. But modern science did not in fact arise in this way. 

This too has its unity, of course a unity derived not from 
deduction but from the homogeneity of its procedure and the 
wonderful, unforeseeable interlocking of its branches over three 
hundred years. Modern science, like medieval science, embraces 
in this unity statements of fact, concepts and theories. It could 
not function if it were not free to employ terms like "electron" 
or "evolution," which are not applicable to crude facts, just as the 

SCIENCE IN 1500 33 

medieval philosopher could not think about plant-life without 
introducing the entity "vegetable soul." Within its own context 
of theory the vegetable soul is not less plausible than the electron, 
and it cannot be said that one or the other can be disposed of 
by a straightforward matter-of-fact test. To do so it would be 
necessary to make a complicated inquiry into the value of the 
factual information supplied by observation and experiment, to 
examine the reasoning involved in either case, to trace the rela- 
tionship between the concept and other elements in the fabric of 
science, and so forth, and it is because modern science in all such 
activities differs from medieval that its fruits are different. From 
such intellectual activities modern science yields a system of ideas, 
not an unlinked series of factual statements, being in this respect 
(despite the immense superiority of its factual content) comparable 
to medieval science. And the latter, as a system of ideas, with all 
the imperfection of its methods and information, was true science. 
It offered a system of explanation, closely related to the facts of 
experience and satisfactory to those who used it, giving them a 
degree of control over their natural resources and allowing them 
to make certain predictions about the course of future events. By 
these standards it was relatively vastly inferior to modern science, 
just as at each stage in its own development modern science has 
been inferior to the science of later stages. But to declare that any 
of its tenets was unscientific is to misuse language. Unscientific 
is a pejorative term meaning inconsistent with the prevailing 
framework of the explanation of natural events and the methods 
used to establish this framework; it can have no other meaning 
because we do not know that what is scientific now will not be 
unscientific in the future. There is no absolute standard. All that 
can rightly be said, when we have understood that medieval men 
had prejudices, purposes and hopes totally different from our 
own, is that they were less inquisitive and self-critical than they 
might have been. They were less interested in natural philosophy, 
for to them it was but a step forward to higher things. Science was 
a means, not an end. 



The subtlety of nature greatly exceeds that of sense and 
understanding; so that those fine meditations, speculations 
and fabrications of mankind are unsound, but there is no one 
to stand by and point it out. And just as the sciences we now 
have are useless for making discoveries of practical use, so the 
present logic is useless for the discovery of the sciences. 1 

IN such terms Francis Bacon, in the early seventeenth century, 
denounced the existing structure of scientific knowledge as he 
knew it. Yet it is clear that the same structure of science had 
satisfied the many medieval philosophers of genius who had ex- 
pounded it; even those who criticized the learning of their day, 
like Roger Bacon, could not depart from its strategic concepts. 
Clearly the difference between the men who taught the Aristo- 
telean world-system and those who later rejected it was not simply 
one of intellectual calibre. Only when the criteria of what consti- 
tutes a satisfactory scientific explanation changed, and when fresh 
demands were made for the practical application of nature's 
hidden powers, could an effective scepticism concerning the 
strategic concepts take shape, as distinct from differences of 
opinion on matters of detail. 2 When such scepticism arose the 
cohesive strength of the science that prevailed in 1500, and on the 
whole throughout the sixteenth century, became significant. 

In modern science the higher-order generalizations are vulner- 
able, but in descending the scale to the substratum of experimental 
fact the chances of serious error steadily diminish. In Aristotelean 
science the reverse was true: an important dogma, such as the 
stability of the earth, might be incapable of experimental proof 

1 Novum Organum, Bk. I, x, xi. 

2 An important change also took place in the idea of hidden powers, as the 
ambition to force "unnatural" operations on nature by esoteric or magical 
means gave way to the belief that man could use processes as yet unknown but 
still strictly rational or mechanistic. 



or disproof (as Galileo himself confessed), but some of the primary 
propositions for example that bodies fall at speeds proportional 
to their weights could be exposed as contrary to experience by 
very simple tests. To modify the accepted scientific opinion of the 
present time it is usually essential to carry out an intricate investi- 
gation verging on the frontiers of knowledge; in attacking the 
conventional science of the sixteenth century it was possible to 
outflank the higher-order generalizations altogether by showing 
that the "facts" deduced from them were simply not true. It 
could not be a fundamental requirement of the world-order that 
changes do not happen in the heavens if the new star of 1572 could 
be shown to be far beyond the sphere of the moon by its lack of 
parallax. This feature in the structure of Aristotelean science de- 
termined a large part of the tactics of the scientific revolution. 
Further, since the unity and cohesion of science were imposed 
from above, growing out of its majestic axiomatic truths, it fol- 
lowed that when the results of any one chain of ratiocination were 
impugned the shock was reflected in similar dependent chains. 
Once it was known that the liver is not the source of the blood- 
stream the whole physiology based on this belief was disposed of 
at one stroke. Admittedly the iconoclasts were not always quick 
to recognize the necessary extent of their destructive criticism 
least of all a Copernicus or a Vesalius which was often jubilantly 
pointed out by their opponents. The weakness of conventional 
science was also its strength; the whole authority of the magnifi- 
cent interlocking system of thought bore down upon an assault at 
any one point. How could a mere mathematician assert the earth's 
motion when a moving earth was absolutely incompatible, not 
only with sound astronomical doctrine, but with the whole 
established body of natural philosophy? Logically, to doubt 
Aristotle on one issue was to doubt him on all, and consequently 
some problems of the scientific revolution, which may now seem 
to involve no more than the substitution of one kind of explanation 
for another, were pregnant with consequence since they implied 
the annihilation of extant learning. 

The sixteenth century shows the tactics of the scientific revolu- 
tion in two contrasted forms. In the year 1543 were published two 
volumes which have become classics of the history of science, the 
De Humani Corporis Fabrica of Andreas Vesalius (1514-64) and the 
De Revolutionibus Orbium Coelestium of Nicholas Copernicus (1473- 


1543). Neither of these books was "modern" in content Vesalius 
was no more successful in escaping the limitations of Galenic 
physiology than Copernicus in departing from the formal system 
of perfect circles but both inspired trains of activity which were 
to lead to the substitution of other conceptions for their own within 
two generations. The two books and their authors, however alike 
in their broad impact upon the scientific movement, are totally 
dissimilar. On the Fabric of the Human Body is a work of descriptive 
reporting; its value depends upon the trained eye of a great 
anatomist and the skill of draughtsman and block-maker, while 
Copernicus' treatise is purely theoretical. Vesalius was a young 
man whose work, if it was his unaided, shows astonishing pre- 
cocity. Copernicus was a dying man, of recognized capacity, who 
had nursed his idea for thirty years. Vesalius' material was taken 
freshly from the dissec ting-table; Copernicus' was the laborious 
digestion of ancient observations. Vesalius was an ambitious and 
popular teacher who contributed to the fame of Padua as a centre 
for the teaching of medicine which lasted till the mid-seventeenth 
century; Copernicus lived obscurely immersed in his ecclesiastical 
administration, hesitant to the last over the enunciation of his 
great hypothesis. The nature of Copernicus' original contribution 
to science is also quite different from that of Vesalius. The former 
was the avowed opponent of an idea, that the earth is the motion- 
less core of the universe, but his opposition rested in no way upon 
his discoveries in practical astronomy, which were negligible, or 
on the precision of his measurements, which was not remarkable. 
It sprang from a demonstrable truth, that celestial observations 
could be equally well accounted for if the earth and planets were 
assumed to move about a fixed sun, allied to various wholly non- 
demonstrable considerations value-judgments seeming to show 
that the astronomical system constructed upon this assumption 
was simpler than the older system and preferable to it. Copernicus 
criticized the internal logic of prevailing ideas, but to be a Coper- 
nican did not add one item to a man's factual knowledge of the 
heavens, whereas it did place him in a position which could be 
challenged on other grounds. Vesalius, on the other hand, gave 
vent to no formidably unorthodox opinions, rather indeed his 
passing comments seem to condemn such innovations. Revering 
Galen as the great master of anatomy, devoting his energies to 
editions of Galen's works, it was with reluctance that Vesalius 


differed from him. Neither theorist nor philosopher, his book 
vastly enhanced the range and precision of knowledge concerning 
the structure of the body, an essential foundation for the rational 
physiology of which he had himself no prevision. In general his 
medical thinking was quite traditional, only his view of what an 
anatomical textbook should be provoked controversy. The publi- 
cation of Harvey's discovery of the circulation of the blood in 
1628 aroused the first serious conflict between ancient and modern 
medical theories. Yet it may be said that the beginnings of the 
scientific revolution are to be found as truly in De Fabrica, and the 
series of illustrated anatomies of which it was the outstanding 
member, as in De Revolutionibus. As examples of types of innovation 
they are complementary. 

The twin advance upon the distinct lines of conceptualization 
and factual discovery constantly occurs in science. The former 
makes the more interesting history, but it must not be forgotten 
that each new observation, each quantitative determination 
accurately made, is adding to the stock of knowledge and playing 
its part in the genesis of a new idea. Indeed, conceptualization can 
only progress and rise above the level of speculation through the 
accumulation of fact by the perfection of techniques of experi- 
ment and observation. Anatomy is the crucial instance of this 
during the early period of the scientific revolution. 

In the middle ages it is difficult to distinguish specialized medi- 
cal sciences from the general practice of the physician and surgeon. 
There was a research interest of a sort in natural philosophy, even 
though the research was of a peculiarly narrow kind and its sole 
instrument formal logic. The medical sciences were even more 
strongly subject to the limitations of the purpose for which they 
were cultivated, the training of medical men. Yet some medieval 
anatomists were imbued with a disinterested love of knowledge, a 
trait which seems to have been stronger in the fourteenth century 
than it was about 1 500. The tradition in medicine was at least as 
tightly unified as that in natural philosophy. The principal auth- 
ority in anatomy, physiology and therapy until the seventeenth 
century was well advanced was that of Galen (A.D. 129-99). 
Other writers on medical subjects were of course studied: in 
clinical matters great respect was accorded to Hippocrates, whose 
works were made more fully known by the humanists. Aristotle 
was also followed in these subjects, sometimes in preference to 


Galen, but it is not easy to underestimate the latter's power. A 
humanist physician, Dr. John Gaius, as President of the College 
of Physicians, could order the imprisonment, until he recanted, of 
a young Oxford doctor who was reported as saying that Galen 
had made mistakes. When men were educated as logicians and 
not as observers it was infinitely easier to detect errors in philo- 
sophy than in anatomy or physiology. Admiration for Galen was 
so extravagant that anatomists were more apt to attribute their 
failure to confirm his descriptions to their own want of skill, than 
to his. 'I cannot sufficiently marvel at my own stupidity,' wrote 
Vesalius, 'I who have so laboured in my love for Galen that I 
have never demonstrated the human head without that of a lamb 
or ox, to show in the latter what I could not find in the former/ 
It was only tardily, and hesitantly, that Vesalius admitted to him- 
self the simple truth that the structure then called the rete mirabile, 
described by Galen in the human head, was a feature not of 
human, but of animal anatomy. 1 Only gradually could anatomists 
learn to see the body otherwise than as Galen had taught them, 
and the broader influence of his pathology lingered well into the 
nineteenth century. Galen was one of the greatest medical scien- 
tists who have ever lived, demonstrating in Rome, some six hundred 
years after Aristotle, the vigour and quality of Hellenistic science. 
He dissected, he experimented and his work, though dominated by 
the vitalistic preconceptions of Aristotle, has a strong experiential 
foundation. He was also an uncritical teleologist, believing that 
it is possible to discover the purpose of every part of the body and 
to prove that it could not be more perfectly designed for that 
purpose. This profound admiration for the divine plan recom- 
mended him strongly to Christian writers of the middle ages. 

In many ways Galen epitomizes the typical qualities of the 
Greek tradition in medieval science, itself often far superior to the 
independent eiforts of the later Latins, but so far imperfect that 
even when it was purified and enriched by renaissance scholars 
a reaction against it was still necessary before modern science 
could take shape. In some aspects the Greek intellect was ' 'modern" ; 
but not in relation to medical subjects. Greek medicine never de- 
tached itself from teleological arguments, and its anatomy was 

1 De Fabrica (1543), P- 642. Quoted by Charles Singer and C. Rabin: A 
Prelude to Modern Science (Cambridge, 1946), p. xliv. Doubts on this point had 
been expressed earlier by Berengario da Carpi. 


always firmly subject to a priori physiological theories, not lending 
itself to the reverse and correct process. There was a deep-seated 
prejudice against human dissection. As a result the study of animal 
anatomy without sufficient check introduced numerous errors. 
Galen worked extensively on the Barbary ape, he may possibly 
have had access to the still-born foetus, but he never dissected an 
adult human subject. This lack of experience was scarcely appreci- 
ated before the time of Vesalius. Technical nomenclature and 
classification were very defective in Greek anatomy, and even had 
description been perfect it would have been useless to a later age 
in the absence of pictorial illustration. At its best the eye of the 
Greek anatomist had often been deceived by his preconceived 
notions of the working of the body. As in astronomy, the Greeks 
had gone far in the direction of precise and careful research, much 
of which proved of enduring value, but the observations they 
made were fitted into a scheme of ideas inherited from primitive 

The influence of Greek texts upon Islamic physicians had 
become considerable by the ninth century A.D., when there was 
much activity in translation. Avicenna (980-1037), the greatest 
scientist of the Arab world and its foremost physician, reproduced 
in his Canon the best features of a Hellenized survey of medicine, as 
well as original observation. To some extent, with its important 
debt to Galen, the Canon replaced Galen's own writings, even in 
the West. Gerard of Cremona in the twelfth century translated it 
and a large part of the Galenic corpus, but not Galen's chief 
anatomical works which were only Latinized in the fourteenth 
century. Other Galenic texts were translated direct from the 
Greek by William of Moerbeke, half a century later than Gerard. 
Eventually, too, all the more important works in Arabic on 
medicine became available, including the Kitab of al-Razi 
(c. 850-924), an even larger encyclopaedia than Avicenna's Canon. 
Before the sixteenth century the Islamic commentaries upon and 
additions to the Greek originals had a decisive influence upon 
the European knowledge of Hellenistic medicine. 

Human dissection was discouraged in Islam. In Europe the 
systematic study of anatomy seems to have begun in the twelfth 
century, contemporaneously with the rise of the famous medical 
school of Salerno, though the practice of actual dissection was a 
north Italian development. The reception of Aristotle's writings 


in the thirteenth century, temporarily interrupting the growth of 
a purely Galenic anatomy and physiology, was counter-balanced 
by a stronger interest in dissection, flourishing under the wider 
privileges of the universities. Dissection was given countenance, 
partly by the needs of surgery, and partly by legal recognition 
(under the influence of the law-school of Bologna) of the value of 
forensic evidence derived from the post-mortem opening of the 
body. There has been at all times and in all places a universal 
revulsion against the dissection of the dead to serve mere curiosity, 
and perhaps it was not extraordinarily strong in the middle ages. 
At least it is likely that human dissection was comparatively com- 
mon at Bologna by the early fourteenth century, the legal post- 
mortem having been transformed into a means of instructing 
students. Henri de Mondeville, in teaching anatomy at Mont- 
pellier in 1304, illustrated his lectures with diagrams probably 
copied from those used in the school at Bologna. 1 

Shortly afterwards, in Mondino dei Luzzi (c. 1275-1326), 
medieval anatomy reached its zenith. He dissected for research, 
and he was probably the first teacher since the third century B.C. 
to demonstrate publicly on the human body. His Anathomia, which 
was printed many times, long remained a popular text. Eager 
to reconcile authorities, he did not venture to assert his own views, 
and perpetuated many mistakes. Good anatomists succeeded 
Mondino (though none escaped his influence) but there was a 
general deterioration in the teaching of the subject. Mondino had 
expounded while at work upon the body; the standard practice 
of a later age is familiar from a number of wood-cuts in early 
printed books. The professor sat in his lofty chair, reading and 
enlarging upon the Galenic text, while an ostensor directed the 
operations of the humble demonstrator who wielded the knife. The 
body again became merely an illustration to the words of nobler 
men. Anatomy degenerated into the repetition of phrases and 
names. No example of the misleading perspective adopted by the 
renaissance scholar could be clearer than this: because he knew 
that the teaching of anatomy had become a literary exercise in 
the fifteenth century, he assumed that it had never been anything 
else, and that the only course was to return directly to the works 
of Galen. 

The curve moves upwards again towards the end of the fifteenth 
1 Charles Singer: The Evolution of Anatomy (London, 1925), p. 73. 


century. One factor in this seems to have been pressure in the 
medical schools for more demonstrative teaching; attendance at 
dissections had .to be restricted so that all might share in the 
spectacle. 1 Another was the official recognition of human dissec- 
tion, under clerical licence, by the Papacy. The first printed 
anatomies with figures appeared in the last decade of the century 
and the first half of the sixteenth shows a whole group of able 
practical anatomists at work Berengario da Carpi, Johannes 
Dryander, Charles Estienne, Canano of Ferrara, Massa, in 
addition to Vesalius. The humanists applied themselves to the 
editing of famous medical texts, and others but recently recovered, 
such as the De re medica of Celsus (first century B.C.), which 
supplemented the medieval corpus. There was a powerful reaction 
against the Arabic authorities, and the Arabic technical nomen- 
clature was gradually replaced by the classical terminology which 
has established itself. Galen's texts were studied in the original 
Greek, and re-translated into Latin. English scholars under the 
patronage of Reginald Pole had a large share in the edition of 
Galen's Opera Omnia printed at Venice in 1525 the connection 
between medicine and philosophy was rediscovered. 2 But scholars 
were not practical anatomists, their enthusiasm reinforced, rather 
than weakened, the medieval attitude to anatomical study. The 
pure Galen still held all Galen's faults, for scholarship could 
purify a text without touching on the errors in observation held 
within it. 

Another and more important source of inspiration was of a 
different kind, the naturalistic movement in art which has already 
been mentioned. Italian artists had been engaged in the study of 
anatomy well before the end of the fifteenth century, and from 
surviving sketches by, for example, Michelangelo or Raphael, it 
appears that they occasionally practised illicit dissection. Leonardo 
da Vinci (1452-1519) certainly did so as his interest in the fabric 
of the body developed from his first attempts to analyse the 
structure of the forms he was portraying. Some of the printed 
anatomical figures of the next generation are indeed reminiscent 
of Leonardo's famous drawings. The representation of anatomical 
structures as seen with the artist's eye and recorded by the artist's 

1 Lynn Thorndike: Science and Thought in the Fifteenth Century (New York, 
1929), p. 69, n. 22. 

2 W. G. Zeeveld: Foundations of Tudor Policy (Harvard, 1948), pp. 53-5. 


pencil, which is totally different from the schematized, diagram- 
matic illustration of an earlier epoch, and even from the merely 
workmanlike but biologically accurate sketches of later professional 
anatomists, thus preceded the work of the founders of modern 
anatomy. The means for duplicating such drawings already 
existed in the technique of wood-cut printing. From this source 
the sense of the actual, of the minute, penetrated into academic 
anatomy and it is significant that the artists were men who had 
no stake in existing theory, and who, in the case of Leonardo at 
least, were unschooled in the textual description of organs. But 
there are limitations to the artistic impulse and to the naturalism 
which is only interested in superficial forms. The artist's drawing 
may not be most suitable for the purposes of a text-book; he needs 
to know something of the configuration and function of the surface 
musculature, of the run of the visible blood-vessels, and perhaps 
something of osteology, but he does not normally need to penetrate 
to the internal organs or the recesses of the skull. The artist at 
the dissecting table would certainly seek to re-create the appear- 
ance of the living body from the structure of the dead but he 
would not usually be interested in the correlation of function and 
the ordering of parts which ultimately lead to the discovery of 
physiological processes. Only when naturalism serves an impulse 
which is no longer purely artistic and has become the instrument 
of scientific curiosity can it have significance for medical anatomy. 
Of course it is abundantly clear that the motive which directed 
Leonardo to make his perceptive and accurate sketches, to take 
casts and prepare specimens by the injection of wax, was of a 
truly scientific order. In him, as in Vesalius, artistic imagination 
was the servant of science. Yet some even of the most naturalistic 
of Leonardo's drawings contain ancient errors, perhaps copied 
from the vernacular anatomical text-books which were already 
available to him: and to the organization of anatomy as a disci- 
pline Leonardo, who had no talent for classification and arrange- 
ment, contributed nothing. In any case the influence of his 
crowded and ill-ordered note-books upon contemporaries is in 
all respects entirely conjectural. 

If the historical situation were that teachers of anatomy and 
medicine in the universities of France and Italy became them- 
selves the pupils of professional artists unlearned in Galen it would 
be unique and surprising. But this was not the situation. It was 


rather that the work of the anatomist reflected, with less artistic 
merit, the same general cultural trend towards naturalism which 
affected purely aesthetic representation more profoundly; and that 
the anatomist made use of the same techniques of draughtsman- 
ship and reproduction as the artist, whose stylistic conventions 
were impressed upon his illustrations. Naturalism, and the desire 
to take advantage of the new faculty of the wood-cut print for 
exposition, forced him along the road to observation. If the teacher 
of anatomy wished to elucidate the Galenic account of the struc- 
ture of the human body by pictures of the features described he 
could do so only by dissecting a body and having drawings made 
he could not reconstruct a picture entirely from a verbal text, 
though the text might influence the instructions he would give 
to the draughtsman. As, in so doing, anatomists observed dis- 
crepancies between the text and the structures themselves they 
departed with greater confidence from the Galenic model and 
learnt to rely on observation alone. A few conservative anatomists 
were well aware of the danger of illustrated texts; too great a 
reliance upon visual images might lead to contempt for Galen's 
superior knowledge. So in fact it happened that Vesalius' cuts are 
sometimes less traditional and more accurate than his text. The 
practice of making realistic not necessarily aesthetically pleasing 
drawings elevated instructional dissection to the level of re- 
search, but in the circumstances of the time opportunities for 
making a recordable dissection were few and hurried. The ambi- 
tion to make (for example) an accurate map of the venous system 
need not be taken to be ipso facto evidence of a critical spirit, 
though it may indicate a more sensitive professional conscience. 
As the first men to embark on such tasks were firmly convinced of 
Galen's rectitude, there was no reason why they should not take 
the liberty to draw what he had already perfectly described. It 
was thus with Vesalius himself: not until his preparatory work 
for the De Fabrica was well advanced did he realize the extent 
to which Galen had transferred animal structures into human 
anatomy. This misleading practice, and Galen's specific mistakes, 
could not be exposed without an impulse to research which in fact 
arose out of the needs of teaching and illustration. The errors in 
text-book anatomy could not be discovered through a desire to 
amend Galen by reference to nature because no one as yet 
believed this to be necessary. 


All this has little relation, directly, to aesthetics. The first illus- 
trated anatomies were not indeed beautiful books, though they 
contained many new discoveries. It may well be that Vesalius' 
superbly produced folio cast an undeserved shadow upon the less 
splendid efforts of his contemporaries and immediate predecessors. 
Perhaps too much emphasis has been placed upon its interest as 
an example of the profitable co-operation between scientist and 
artist in the sixteenth century; certainly Vesalius' figures were fine 
enough to prompt frequent plagiarism. The preparation of illus- 
trated anatomies demanded such a collaboration, and provided 
an incentive for an original research, but Vesalius was not the first 
to attempt a complete pictorial survey, which he began with 
youthful energy. When in 1537 he set to work on De Fabrica, and 
commenced teaching anatomy at Padua, Vesalius was twenty- 
three. He could hardly claim to write with mature knowledge, 
and though he had studied medicine at Louvain and Paris, so far 
as is known his experience of dissection was still very limited. Nor 
was he qualified to stand as an arbiter between Galen and Nature, 
for at Paris especially, under medical humanists who were un- 
shaken followers of Galen, he had been well grounded in the 
renewed Greek tradition. Vesalius' first notable publication was 
a revision of Johann Giinther's Anatomical Institutions according to 
Galen (1538), and his second, the Tabula Sex, was a series of wood- 
cuts to illustrate the Galenic exposition of human anatomy which, 
though based on dissection, was still traditional in character and 
repeated many ancient mistakes. It was not, apparently, until the 
preparation of De Fabrica was well advanced (about 1539-40) that 
Vesalius began to doubt whether an anatomy founded on natural- 
istic illustration could be reconciled with Galen's descriptions. 
Even of Vesalius' finished work it has been said that: 'A few of 
his comments reveal an active dissector less experienced than 
his contemporaries Berengario da Carpi, Massa and Charles 
Estienne.' 1 

Creative scientific ability may run strongly in the direction 
either of practical work or of theory. To the former talent the 
medieval world offered little opportunity in comparison with that 
offered by modern experimental science. As mechanics was in the 
early seventeenth century the ideal field for the exercise of the 

1 Charles Singer: Studies and Essays in the History of Science and Learning offered 
to George Sarton (New York, 1947), P- 47* 


conceptual intellect of Galileo, so anatomy in the sixteenth was a 
fruitful subject for keenness of observation and, to a less degree, 
ingenuity of experiment. Unconsciously the new developments in 
the study of anatomy ran counter to the humanistic endeavour. 
At the very moment when humanists were rediscovering the 
philosopher in Galen his scientific authority was being under- 
mined. As with so much original effort in the first stages of the 
scientific revolution, a more perfect anatomical knowledge con- 
tributed not to the integration of science but to its disintegration, 
in this case to the elaboration of a specialized art of detached 
description through which alone accuracy could be attained. The 
anatomists who freed themselves, however partially, from their 
natural inclination to follow classical masters were framing a new 
standard of scientific observation. In no real sense was this the 
moment of the birth of some novel, self-conscious method of 
observation and experiment in science, but it was the moment 
when the accepted narrative of fact and theory was first modified 
effectively and permanently by recourse to nature. A body of 
original facts relating to a single discipline was for the first time 
gathered together for comparison with the traditional account. 
Justified only by practical experience, even opposed to the theories 
of those who described them, the new discoveries combined to 
teach the lesson that the whole doctrine of anatomy must be re- 
formed by the use of meticulous observation and independent 
thinking. While the facts of experience to which appeal had been 
made in the framing of medieval physical theories had mostly 
been commonplace, or accidentally revealed, the new anatomy 
turned to the systematic exploitation of a specialized and laborious 

The most complete, and the most striking, use of this technique 
was certainly in the De Fabrica of Vesalius. All authorities on the 
subject agree that Vesalius' exposition of human anatomy is out- 
standing in early modern times, basing their judgement on his text 
as well as on his still more eloquent illustrations. But he was not 
unique in his originality; rather he was the most successful ex- 
ponent of a new procedure that was beginning to gain adherents 
over all Europe, some of whom Vesalius did not scruple to treat 
unfairly. Among his immediate predecessors Berengario, whose 
illustrated Commentary on the anatomy of Mondino was published 
as early as 1521, was notable for hesitancy in following Galen. 


Another, Charles Estienne, was at work on his book On Dissection 
by 1532, though this remained imprinted till I545- 1 Estienne was 
the first anatomist (after Leonardo) to prepare figures illustrating 
complete systems (venous, arterial, nervous) and he discovered 
the structures in the veins, later known to be valves, which stimu- 
lated William Harvey to the discovery of the circulation of the 
blood. John Dryander published two illustrated treatises in 1537 
and 1541. Canano's incomplete myology also appeared in the 
latter year (or 1540), and nine years after the publication of De 
Fabrica, a set of copper-plates to illustrate human anatomy was 
finished by Bartolomeo Eustachio (1520-74), which have been 
described as more accurate than Vesalius' figures, and almost 
equally crowded with new observations. 2 Some of the unillus- 
trated treatises on anatomy, such as those of Sylvius and Massa, 
are not less remarkable for skill in dissection and acuity in criti- 
cism. Moreover, in the application of anatomical knowledge to 
physiological theories a subject in which Vesalius was steadily 
conservative another contemporary, Jean Fernel (1497-1558), 
was far in advance of his time; and, soon after 1543, Serveto, 
Colombo and Fallopio were putting forward notions on the dis- 
tribution of the blood about the body of which no hint is to be 
found in De Fabrica. 

When Vesalius is matched against his not unworthy rivals, his 
peculiar fame appears all the more enigmatic. He did not lead 
the way in making discoveries alien to Galenic anatomy, nor did 
he ever intend an onslaught upon it. He had no greater learning, 
or more vivid freshness of mind, than his more experienced con- 
temporaries. Even when spoken of by his teacher Giinther as 'a 
young man, by Hercules, of great promise . . . very skilled in dis- 
secting bodies,' the observation for which he was thus praised had 
already been anticipated in Italy. The task which he set himself 
would seem to require ample time and mature knowledge, but 
Vesalius had neither. During the mere three or four years given 
to De Fabrica he was busy with other writing, teaching and travel. 
His whole study of female anatomy was based on the hasty dis- 

1 De dissections partium corporis humani, a large octavo, has fifty -eight full-page 
wood-cuts, in which unfortunately the important portions are often too small 
to be clear. 

2 Charles Singer: Evolution of Anatomy, p. 135. Eustachio's figures, after being 
first printed in the early eighteenth century, were thereafter frequently 
republished as having contemporary value. 


section of three bodies not surprisingly, it forms one of the weakest 
portions of his work. Comparison of the Tabula Sex with De Fabrica 
compresses his development as a scientist into an almost incredibly 
brief space of time, if it was entirely unaided. Little is known of 
his personality; in comparison the biography of Copernicus is 
full. Often abusive, truculent, Vesalius was not a learned man by 
the standards of his age, and he reveals little in the way of philo- 
sophic depth such as was then expected of a scientist. He was am- 
bitious, and apparently ambition prompted his one great work; 
after leaving Padua in 1543 to become an Imperial physician his 
career in science ended. 

It is impossible to fit Vesalius into the conventional picture of 
the scientific worthy. But whatever may be the truth concerning 
the collaboration of artist and anatomist in the production of De 
Fabrica, however serious the charges that may be brought against 
Vesalius' character as an author, the book itself stands as a monu- 
mental achievement of sixteenth-century science, and in its own 
time it was almost immediately recognized as such. De Fabrica was 
the implementation, in a manner whose total effect is superior to 
that of any contemporary work, of a single conception of what an 
anatomical treatise ought to be, and there is no evidence that this 
conception was not Vesalius' own. It aimed at a systematic, illus- 
trated survey of the body part by part, layer by layer. The skeleton 
and the articulation of joints, the muscles, the vascular system, the 
nervous system, the abdominal organs, the heart and lungs, the 
brain, were described and depicted with a detailed accuracy never 
previously attained. The wood-cuts are indeed on occasion better 
than the text they illustrate, though in one place it is admitted that 
a drawing had been modified to fit Galen's words. In his section 
on the heart Vesalius mentions probing the pits in the septum 
without finding a passage; broadly, however, he accepted the 
Galenic account of the heart's function. Some whole topics (the 
female organs, the eye) were less well discussed owing to errors in 
observation, due in part to Vesalius' inability to free himself com- 
pletely from traditional ideas. In minutiae there was much for the 
anatomists of the later sixteenth century to amend. 

As a reformer despite himself, Vesalius' attitude to orthodox 
instruction was cautious. Where his departures from Galen's texts 
are most notable, generally he said little more than others at the 
same time were saying. 


If it be said that he often corrected Galen it may be rejoined that 
much more often he follows Galen's errors. , . . The Fabrica is, in 
effect, Galen with certain highly significant Renaissance additions. 
The most obvious and the most important is the superb application 
of the graphic method. 1 

But the graphic method was not invented by Vesalius, and to what 
extent its quality was due to the draughtsman employed (who, 
according to the art-historian Vasari, was John Stephen of Calcar) 2 
will probably never be known. Although Vesalius hotly criticized 
Galen for describing human anatomy by analogies drawn from 
animal dissection, he was himself led into mistakes resulting from 
this very practice. In his interpretation of the functions of the 
structures described he followed Galen closely. His boastful narra- 
tive of his own achievements, and his claims to originality are not 
to be trusted without scrutiny; thus it is obviously untrue that 
human dissection was utterly unknown in Italy before he intro- 
duced it at Padua. Vesalius seems to have resented, rather than 
welcomed, originality in other anatomists. It is true that both his 
successors at Padua, Realdo Colombo (who had worked with 
Vesalius) and Fallopio, made important additions to knowledge, 
but Vesalius himself launched an attack upon the latter's innova- 
tions. The tradition of anatomical study was not inaugurated in 
northern Italy by Vesalius during his short residence there, for 
it had existed for centuries. As for the claim that Vesalius was the 
first teacher of anatomy in modern times to carry out dissections 
before the students with his own hands the idealized scene is 
represented in the frontispiece to De Fabrica the view has recently 
been put forward that even as early as 1528, and in the humanistic 
medical school of Paris, ' the participation of students and doctors 
in the actual process of dissection was recognized.' 3 It seems, 
therefore, that if Vesalius introduced any new teaching method to 
Padua it was but the method he had known at Paris. 

In him there was neither the burning passion of a Galileo to 
refine truth from error, nor the remote vision of a Kepler; yet the 
work of a man whose spirit is calm, almost plodding, may mark a 

1 Charles Singer: Studies and Essays in the History of Science and Learning offered 
to George Sarton (New York, 1947), p. 81. 

2 This attribution has been disputed and defended; cf. W. M. Ivins in Three 
Vesalian Essays (New York, 1952). 

3 Charles Singer: Bulletin of the History of Medicine, vol. XVII (Baltimore, 


turning-point in exact science. If Vesalius was pre-eminent among 
early anatomists he must not be made so at the expense of his 
contemporaries, who were also men of ability and precision, nor 
by neglecting his own faults and mistakes. Although the structure 
of De Fabrica was excellent, Vesalius was a poor expositor; 
nevertheless, his text inculcated the principles of the new mode of 
anatomical study more effectively than any other work, and 
brought back the study of anatomy to the dissecting-table. He was 
responsible for making many useful innovations in the technique 
of dissection which extended its possibilities. He had the merit of 
seeing anatomy as more than a catalogue of structures useful to the 
physician seeking the proper vein from which to let blood or to 
the surgeon tracing the course of a bullet- wound; it was for him 
an entrance into knowledge of the living body as a functional 
organism. True, he was unable himself to progress far towards 
this desideratum, and therefore he was content to rely upon 
Galen, but his work was a guide to his successors. De Fabrica must 
be judged as a whole, and it is in the preponderance of its virtues 
over its defects that the book excels. In a descriptive subject such 
as anatomy, especially where the relations between the possibilities 
of research and the necessities of teaching are very close, there 
seems to exist a critical level of accuracy. Until description has 
passed the critical point no steady accumulation of knowledge is 
possible because there is no firm orientation to study, no sound 
model exists, doubt and duplication lead to wasted effort and 
repeated surveys of the same elementary facts. Once the critical 
point is passed and the outline is securely drawn, so that the 
student can easily identify it with the natural subject, it is possible 
to press forward to deeper and finer levels of detail. Vesalius 5 
contemporaries had almost attained this point; in particular 
studies some passed far beyond it; but De Fabrica passed it in an 
extended account of the whole body. The work was far from 
impeccable, perhaps its originality and the importance of a high 
aesthetic (which is not the same as a naturalistic) quality in its 
illustration have been over-emphasized, but it was sufficient. 1 
The map was made. It is not enough to say that Vesalius 

1 There are some hundreds of figures, not including the initials, in the first 
edition of the De Fabrica. Of these, only about a score enter the "aesthetic** 
class: they are, of course, the finest wood-cuts in the book, but they do not 
compose the whole of Vesalius' graphic teaching. 



redirected anatomists to the natural facts of bodily structure, for 
the work of contemporary anatomists was already in the same 
direction, and in any case it was to be long before the meaning of 
these facts (like the valves in the veins) could be correctly inter- 
preted. The main point is that the De Fabrica was the actual 
source from which the method of obtaining the facts of human 
anatomy by dissection and experiment was learnt; admittedly 
it could still have been learnt had the De Fabrica never been 
printed. In the hands of students it was an instrument fit to 
measure against nature, to serve as a guide to the complexities 
which Vesalius' successors discovered in their turn, and to create 
in the exceptional man the critical frame of mind which is the 
main-spring of research. 

In a sense the possession of this quality belongs to the definition 
of modern science. In many instances the reason for the sterility 
of conventional science before 1500 was not simply that its 
exponents were engaged upon a vain endeavour, nor most 
obviously that they were fondly prejudiced, perverse, or unoriginal 
of mind. They, like all men, could do no more than accept or 
modify according to their powers an intellectual inheritance 
which was a part of the age and society in which they lived. Such 
an inheritance is never exactly consistent, nor is it wholly dominant 
over the individual, but the range of possible variation from it is 
always limited. One characteristic of the intellectual heritage of 
every medieval philosopher, or physician, was the limited area of 
contact between the system of ideas in science and the reality 
of nature; on the one hand was a natural philosophy satisfactory 
enough to those who knew no other, and on the other the bewilder- 
ing complexity of the natural world. A juxtaposition of the two 
was not easily effected. If it seemed that philosophy explained the 
world, it seemed so because the distinction between the philosophic 
view of natural phenomena, and the phenomena themselves, was 
not clearly revealed; and since the globus intellectualis and the 
globus mundi were so far distant, constructive, purposeful criticism 
of the former could hardly emerge from its comparison with the 
latter. Hence arises the importance of a new field of experience, 
such as magnetism offered to the middle ages, or of a new attitude 
to scientific explanation, such as that contained in the mechanistic 
philosophy of nature. The effect of every major idea in science, of 
every major observation and experiment, has been to present a 


new juxtaposition of the realm of thought and the realm of facts, 
which may in turn demand a far more profound readjustment 
than the original innovator could foresee. 

It is easier to illustrate this from the history of ideas than from 
the history of factual discoveries, easier to see it in Copernicus, 
for example, than in Vesalius. It is obvious now that once the 
central tenet of the old astronomy was rejected, the incidentals 
which Copernicus had retained must also be challenged. Yet it is 
important, for the understanding of the process and development 
of the scientific revolution, to see how the cardinal observations 
and measurements emerged, as well as the cardinal concepts. The 
normal development of any established department of science may 
be, and indeed usually is, conditioned in large part by its con- 
ceptual structure and the nature of the theoretical techniques 
appropriate to it, since these furnish the perspective in which the 
problems are to be seen. In exceptional situations, however, the 
disclosure of a new fact commonly the apprehension of the im- 
port of a whole group of facts may force a crisis. Then existing 
theory may prove an obstruction. A novel perspective is called 
for. In this respect stands the work of Vesalius to that of Harvey 
and later physiologists, who revolutionized ideas by applying 
experimental procedures to the elucidation of the bare facts 
yielded by a more exact anatomy. Through the effort of Vesalius 
and his less famous contemporaries there was introduced into 
biological science for the first time an acute sense of the importance 
of minutiae, of the mastery of special methods, and of the precise 
and full reporting of observations. Contemporaries admired the 
De Fabrica as the perfection of descriptive art, to this also its claim 
to mark a turning-point in the growth of scientific knowledge is 
due. But the book is not less notable as entailing the challenge to 
Galenic theory which its author scarcely contemplated. 

De Revolutionibus Orbium Coelestium has an altogether different 
character. Its force springs from the other tactic of the scientific 
revolution, accepting the body of observation on which conven- 
tional science relied and even the method by which the facts 
could be grouped into a theoretical interpretation, but denying 
that only the conventional interpretation was possible, or even 
preferable to its alternative. Although his name has become more 
famous, Copernicus was in many ways less modern than Vesalius, 
in particular he had a far less acute sense of the reality of nature: 


like many medieval men he was far more concerned to devise a 
theory which should fit an uncritically collected series of obser- 
vations than to examine the quality of the observational material. 
Tycho Brahe, half a century later, was the Vesalius of astronomy. 
If one can discern a fundamental motive for Copernicus' 
reconstruction of the cosmos, that too seems to be medieval. 
The unity of thought had been the goal of medieval philosophy: 
the harmonizing of pagan science and Christian religion, the re- 
conciliation of authorities, the explaining of contradictions and 
discrepancies, had been its unending task. And it seems that the 
belief that true knowledge must be unified provoked Copernicus' 
first doubts. The early sixteenth century was not a time at which 
dogmatism on astronomical problems was easy or profitable. The 
popular view that the astronomical science of the middle ages 
was simply a matter of applying rigid principles in a determined 
fashion is mistaken. Of course the main structure of astronomical 
theory was firmly established, but the working out of the exact 
details involved constant experimentation, and the best authors 
were not themselves agreed on the true values to be attached 
to all the constants of the Ptolemaic system. In fact medieval 
astronomers were well aware that that system was not meticulously 
accurate as a calculating instrument and, though they did not 
revolt against its fundamentals, they attempted by adjustments 
and additions to bring it to perfection. Wherever astronomy was 
actively studied, there was a renewed interest in observation, 
in modifications to the machinery of the spheres, and renewed 
computation of the constants and tables. The greatest problem of 
all was of a different order. No man of learning could ignore the 
fact that the system of Ptolemy was something more than an 
elaboration of that of Aristotle. To describe as physical the 
Aristotelean picture of the cosmos, and to describe the Ptolemaic 
as a mathematical hypothesis of planetary motions, is perhaps to 
press an analysis of which the middle ages were barely conscious. 
Yet, while there was no direct or irresolvable antithesis, it was 
always clear that there was something of a hiatus between 
cosmological physics and astronomy. There was not merely a 
perpetual struggle to reduce the complexities of planetary motion 
to mathematical order, but also these complexities were confusing 
in physics. The eccentricity of the earth with respect to certain 
spheres, and the irregularity of the motion of these spheres about 


the earth, were assumptions which practical astronomers were 
forced to make, without possibility of reconciliation with Aristotle's 
physical doctrine. Oresme pointed out another difficulty that 
arose from the introduction of epicycles, concluding that Aristotle 
was obviously mistaken in his demonstration that the intelligences 
controlling the spheres do not themselves move. 1 He seems to 
distinguish, too, between what is true "in philosophy" and true 
"in astrology," i.e. astronomy. In more practical ways the im- 
perfections of astronomy were recognized. The calendar was out 
of joint. Even astrologers admitted that their calculations were 
uncertain because of the inaccuracy of the tables with which they 
worked. Tables for the cycle of moon and tides, essential to seamen, 
were unreliable. The observational basis in the celestial coordin- 
ates of the fixed stars, and the latitudes of places on the earth, was 
equally open to doubt. Humanism added its own confusion: the 
conflict between Arabists and Humanists was less spectacular in 
astronomy than in medicine, but it was not the less real in the 
difference of opinion between those who wished to preserve the 
simpler system of Ptolemy, and those who believed that Islamic 
elaborations, like the trepidation of Thabit, were necessary. 

Already in the fifteenth century Peurbach and Regiomontanus 
had applied themselves to the technique of observation, and tried 
like their predecessors to bring astronomy up to date by new 
determinations and computations. They did not appeal to nature 
against Ptolemy, but they sought to refresh his system by a new 
draught of observation. The world of learning upon which 
Copernicus entered knew that a reform was needful, even though 
it did not welcome the shape of that reform in his hands. A world 
expecting some new mathematical formula which would u save 
the phenomena" along the old lines received instead an unprece- 
dented synthesis of philosophy and mathematical astronomy 
which attacked much that was orthodox in both. Although united 
in the higher realm of ideas, the philosopher and astronomer 
had long been professionally divorced. Those who contemplated 
the mysteries of the cosmos had done little actual observing or 
calculating, while the practical astronomer had lost himself in 
mathematical abstractions. Copernicus was a superbly equipped 
theoretical astronomer (with some skill in observation, but no 
great love for it) who shows at the same time a strong sense of 
1 Medieval Studies, vol. IV, p. 169. 


physical reality. He was affronted by the Aristotle-Ptolemy 
dualism. He thought that some of the devices used by Ptolemy, 
especially the equant-point, were cheats counter to sound 
philosophy. He found that the physical system failed in mathe- 
matics, the mathematical in physics. The only solution to the 
dilemma required two steps: the purging from mathematical 
astronomy of its needless reduplications, and from physics of 
those ideas which were obstacles to a true conception of the 
universe. Thus the reform of astronomy demanded a limited 
reform of physics, and Copernicus was in fact impelled to dis- 
tinguish between those doctrines of Aristotelean physics which he 
took to be true, and those which he took to be false. In the end 
much was to turn upon the justice of his conception of what is 
"right" in nature. 

There is good evidence that Copernicus was highly esteemed 
by men of learning long before the publication of De Revolutionibus, 
which indeed in the eyes of some contemporaries diminished rather 
than enhanced his reputation. 1 Rheticus describes him as 'not 
so much the pupil as the assistant and witness of observations' 
of Domenico Maria da Novara, himself something of a critic of 
Ptolemy, at Bologna: and as lecturing on mathematics at Rome 
in 1500 (when he was twenty-seven) 'before a large audience of 
students and a throng of great men and experts in this branch of 
knowledge.' 2 Clearly Copernicus had already become an accom- 
plished student of mathematics and astronomy in his earlier days 
at Cracow. On his second visit to Italy in 1514 he was consulted 
on the question of calendar reform. One of his critical writings, 
the Letter against Werner (1524), seems to have circulated in 
manuscript, as did the first sketch of his new astronomy, the Little 
Commentary which was written, probably, about 1530. There is a 
record of Copernicus' ideas being explained to Pope Clement VII 
in 1533. In 1539 his fame attracted the Protestant Georg Rheticus 
from Wittenberg to Frauenberg, "remotissimo angulo terrae," to 
become his pupil, and in the following year Rheticus' First Account, 
a review of Copernicus' manuscript of De Revolutionibus, was 
published at Dantzig. Some of his readers, who like Gemma 
Frisius and Erasmus Reinhold later became firm advocates of 

1 Lynn Thorndike: History of Magic and Experimental Science, vol. V (Balti- 
more, 1941), pp. 408-13. 

2 Edward Rosen: Three Copernican Treatises (New York, 1939), p. in. 


the heliostatic system, awaited the publication of the whole work 
with eager anticipation. In the preface to his book, dedicated to 
Pope Paul III, Copernicus particularly mentions, as friends who 
removed his reluctance to publish, Nicholas Schoenberg, Cardinal 
of Capua and Tiedeman Giese, Bishop of Culm. While his 
investigations thus received a measure of countenance at Rome, 
it was Luther who was to speak of 'the fool who would overturn 
the whole science of astronomy.' 1 

Despite this, the new doctrine failed to secure adherents. 
Favourable references to it are scarce throughout the sixteenth 
century: most are couched in terms resembling Luther's. 2 
Admittedly the book was difficult, written only for those who were 
skilled geometers and experienced in astronomical calculation, 
and it supported a proposition which had been condemned in 
philosophy for two thousand years, and no astronomical advan- 
tages even if they were genuine could vindicate it. If the 
celebrated note by the Lutheran minister Osiandcr which, 
unknown to Copernicus, declared that the tenets of the following 
book were to be taken only as a mathematical hypothesis, a 
calculating device, and not as truth, had any effect in warding 
off official censure (which seems doubtful), it certainly did nothing 
to weaken the general sentiment that speculation on the earth's 
movement was foolish and futile. Those who are known to have 
held the opposite view in the years 1543-60 can be numbered on 
the fingers of one hand: Reinhold, who calculated the first set 
of astronomical tables in accordance with Copernican theory; 
Robert Recorde, the English mathematician; John Field and 
John Dee, English astronomers; and Gemma Frisius of Louvain, 
one of the most famous astronomers of the age. 3 There is nothing, 
other than Copernicus' own book, that can be called an exposition 
of the heliostatic hypothesis in the later sixteenth century. Until 
after the condemnation of Giordano Bruno in 1600 Copernicus' 
name was suppressed not by authority, but by indifference. 

To understand this, it is necessary to understand in what 
measure De Revolutionibus was revolutionary, and effected a 
reform in astronomical thought. In the heliostatic principle, and 

1 De Revolutionibus Orbium Coelestium (Nuremburg, 1543), sig. iii recto. 

2 Dorothy Stimson: The Gradual Acceptance of the Copernican Hypothesis (New 
York, 1917). 

3 Gf. Grant McGolley: " An early friend of the Gopernican theory : Gemma 
Frisius," Isis, vol. XXVI (1937), p. 322. 


in its necessary physical consequences, Copernicus opposed the 
common sense of his age: in everything else he was conservative. 
There was nothing in the method of his madness to arouse 
contemporary interest. Moreover his madness took the form of a 
familiar heresy: therefore again the whole theory could be lightly 
dismissed. A whole stream of references proves that to suppose 
that the sixteenth century ought to have reacted violently in 
approval or condemnation of the book when it appeared is to 
misunderstand a whole facet of medieval astronomy. That certain 
of the ancients had supposed the earth to move was as well known 
to the middle ages as Aristotle's powerful reasoning against their 
contentions. 1 They found the question debated again by their 
Arabic authorities. As a result, several scholars of the fourteenth 
century exhibit a marked tolerance in their treatment of the idea 
when commenting upon Aristotle, among them many members of 
the " impetus" or experimentalist school, including William of 
Ockham, Albert of Saxony, Jean Buridan, and Nicole Oresme. 
Oresme, in his commentary on De caelo, denies that the stability 
of the earth is a logical consequence of the movement of the skies: 
from the analogy of a revolving wheel he shows that it is only 
necessary in circular motion that an imaginary mathematical 
point at the centre be at rest. Further he says that local (i.e. 
relative) motion need not necessarily be referred to some fixed 
point or body: rest is the privation of motion, and is in no way 
involved in its definition. For instance, he says, there is imagined 
to be outside the universe an infinite motionless space, and it is 
possible that the whole universe is moving through this space in 
a straight line. To declare the contrary is an article condemned 
at Paris, yet this motion could not be considered to be relative to 
any other fixed body. Suppose that the skies stood still for a day 
and the earth moved: then everything would be as it was before. 2 
In another place he gives his judgement, "under all correction," 
that it is possible to maintain and support the opinion that it is 
the earth which is moved with a daily motion (axial rotation) and 
not the sky, and further that it is impossible to prove the contrary 
by any experiment ("experience"), or by any reasoning. This 
was just what Galileo was to declare nearly three hundred years 
later. Against his proposition Oresme quotes three arguments, 

1 McColley: " The theory of the diurnal rotation of the earth," ibid. p. 392. 

2 Medieval Studies, vol. IV, pp. 203-7. 


all*of which were to be directed against the Copernican hypothesis 
in the sixteenth and seventeenth centuries. Firstly, the skies are 
actually observed to revolve about their polar axis; secondly, if 
the earth turned through the air from west to east, a great wind 
would be felt constantly from the east; and thirdly a stone thrown 
vertically upwards would not fall back at the place whence it was 
thrown, but far to the west. Oresme has replies to all these objec- 
tions. In answer to the first, he emphasizes the relativity of all 
appearance of motion: a man seated in a boat gazing at another 
boat cannot tell whether his own vessel is moving, or the other in 
the opposite direction, but there is a prejudice in favour of the 
stability of one's own immediate frame of reference. As for the 
wind, the earth, water and air of the sublunary world all move 
together, and so there is no wind other than those to which we are 
accustomed. To the third objection Oresme replies that the stone 
thrown up in the air is still carried along in the west-east direction 
with the air itself, and with ' all the mass of the lower part of the 
world which is moved in the daily movement.' It is not quite 
clear what this last phrase meant to Oresme, but it holds an idea 
of profound consequence. The stone falls back to the place whence 
it came, as it would do if the earth were still, and Oresme points 
out (again anticipating Galileo) that all the phenomena of motion 
appear to be identical in a ship which is moving or a ship which 
is at rest. As Oresme puts it, in less precise language, a movement 
which is compounded of motions in two directions is not discern- 
ible as such when the observer himself participates in one of 

Various theoretical or physical arguments against the rotation 
of the earth anticipated by Oresme turn upon the idea that it 
would be unnatural and out of place in the texture of natural 
philosophy. This Oresme also denies. He points out that the 
Aristotelean system attributes no movement to the earth as a 
whole, though Aristotle himself declared that a single simple 
motion was appropriate to each element so that the earth might 
well turn in its place, as the heavens do, or as the element fire 
does. Oresme agrees that if the earth turns it must possess a "mov- 
ing virtue," but this it must have already, since displaced parts of 
the earth return to it. To the criticism that the motion of a moving 
earth would falsify astrology, he makes a most important riposte. 
All conjunctions, oppositions and influences of the sky would take 


lace as before, and the tables of the movements of the heavenly 
Ddies and other books would be as true as they were before, only 
would now be recognized that the daily rotation was apparent 
[ the heavens, and real in the earth. It has often been alleged 
iat Copernicus destroyed whatever scientific basis astrology 
dght be supposed to have had. It was not so. The practice of 
itrology has been entirely unaffected by it, just as it was (and is) 
naffected by the fact that the "Houses" of the zodiac no longer 
xrrespond with the constellations after which they were named 
ying to the precession of the equinoxes. The predictions of 
dicial astrology turn upon the configuration of the skies at any 
oment: they are unconcerned with the mechanics of the motions 
i which those configurations are produced. And Oresme's dis- 
aimer was actually re-echoed in the sixteenth century. To quote 
horndike: 'It is a historic fact that the Copernican system was 
*st publicly announced, if not precisely under astrological aus- 
ces at least to an astrological accompaniment and that such 
unifying the future was for long after associated with it in men's 
inds.' 1 Two of the leading exponents of the new scheme, 
heticus and Reinhold, had no doubts of the virtues of judicial 
trology, and Copernicus himself never declared against it. 
The authority of Scripture was constantly brought to bear in 
vour of the geostatic doctrine, but even this does not silence 
resme. Joshua's miracle can be interpreted in the sense that the 
n apparently stood still, while the earth was really halted. He seizes 
Don the point that if the earth be supposed to move from west to 
ist, all the celestial motions will take place in the same sense, 
hich he thinks increases the harmony of the system. Also it would 
ace the habitable part of the globe on the right or noble side of 
.e earth. Again, it will be found that in this way the celestial 
)dies which are farthest from the centre will make their circuits 
ore slowly (instead of more quickly as in the geostatic theory) 
hich seems reasonable; and the principle that God and Nature 
) nothing in vain will be more faithfully observed; for example, 
iere will be no necessity for a ninth sphere. After all this potent 
asoning has been marshalled against the conventional doctrine, 
comes as an anticlimax to find Oresme returning to it. c Never- 
teless/ he concludes, 'all maintain, and I believe, that the 
ravens are thus moved, and the earth not: "for God fixed the orb 
1 Op. cit., vol. V, p. 414. 


of the earth, which shall not be moved," 1 notwithstanding the 
reasons to the contrary, for these are not conclusive arguments. 
But considering all that has been said, one might believe from this 
that the earth is moved, and the sky not, and there is nothing 
obviously to the contrary, which seems prima facie as much, or 
more, against natural reason as are the articles of our faith.' 2 

One might think that the famous cosmological debate of the 
seventeenth century had been rehearsed in the fourteenth! 3 There 
were, indeed, subtle changes in the background in which Galileo 
set the same, or similar, arguments; but if Oresme had been dili- 
gently followed the stability of the earth could hardly have been 
defended save as an act of faith, not by reason and observation. 
The diurnal revolution was again discussed in the fifteenth century, 
when it was upheld by Nicholas of Cusa, and in the early sixteenth 
before the appearance of De Revolutionibus. This diurnal revolution, 
however, and the long argument in favour of it by Oresme, must 
be clearly distinguished from the theory of the annual motion of 
the earth which was developed by Copernicus, not to speak of the 
third motion which he attributed to it to account for the parallel- 
ism of its axis in space. A heliostatic theory imposed a far more 
severe strain on intellectual adaptability than a geocentric theory 
which admitted the diurnal rotation. To have conceived the 
annual motion is Copernicus' chief claim to originality, and it was 
the annual motion which condemned the Copernican hypothesis 
both in the eyes of the majority, and also in the eyes of the Church 
because of its heretical consequences. 

It can hardly be imagined that the earlier discussion of the 
diurnal motion was unknown to Copernicus, and he must have 
considered its adoption as the first step to a reform of astronomy 
a step which unfortunately did little to solve the problem of 
planetary motions and the multiplicity of spheres. It is not unlikely 
that his conception of the earth as of the same kind as the heavenly 
bodies, and therefore equally suited "by nature" to planetary 
motion (being spherical for instance), is an extrapolation from the 
reasoning used (by Oresme among others) to support the idea 
that the earth is "by nature" suited to axial rotation. Certainly 

1 Psalm XCIII, i : 'The world also is stablished, that it cannot be moved.' 

2 Medieval Studies, vol. V, pp. 271-9. 

3 As was long ago pointed out, with too great emphasis and some misunder- 
standing, by Duhem in Revue Generate des Sciences Pures et Applique'es, vol. XX 


Copernicus had to abandon the idea of "one element, one motion," 
but this had been virtually abandoned by Oresme. Not, however, 
until Copernicus had begun to consider this second, annual 
motion could he have begun to see the possibility of results im- 
portant to mathematical astronomy in this the middle ages had 
done little or nothing to help him. Even Oresme's very correct 
remarks on the illusions of relative motion only refer to a geo- 
centric system, though they were equally valid as Copernicus 
applied them to the heliocentric. Unfortunately, the steps by 
which Copernicus proceeded from the first to the second motion, 
if that was his course, are totally unrecorded. He relates simply, in 
the Preface to his book, 

Nothing urged me to think out some other way of calculating the 
motions of the spheres of the world but the fact that, as I knew, 
mathematicians did not agree among themselves in these researches. 
For in the first place they are so far uncertain of the motion of the 
Sun and Moon that they cannot observe and demonstrate the 
constant magnitude of the tropical year. 

Then he goes on to say that there was no consistency of principle 
in the devices that had been used some had employed the simple 
homocentric spheres, others eccentric spheres, and yet others epi- 
cyclic systems. They had passed over the symmetry of the universe, 
as though one should put together a body from different members 
in no way corresponding to one another, so that the result would 
be rather a monster than a man. This uncertainty, he thought, 
must prove that some mistake had been made, otherwise every- 
thing would have been verified beyond doubt. 

Then when I pondered over this uncertainty of traditional mathe- 
matics in the ordering of the motions of the spheres of the orb, I was 
disappointed to find that no more reliable explanation of the mechan- 
ism of the universe, founded on our account by the best and most 
regular Artificer of all, was established by the philosophers who have 
so exquisitely investigated other minute details concerning the orb. 
For this reason I took up the task of re-reading the books of all the 
philosophers which I could procure, exploring whether any one had 
supposed the motion of the spheres of the world to be different from 
those adopted by the academic mathematicians. 

Coming across Greek theories which attributed both an axial 
and a progressive rotation to the earth, and following the example 


of his predecessors who had not scrupled to imagine the circles 
they required to "save the phenomena," he thought he might 
himself be allowed to try whether, by allowing the earth to move, 
more conclusive demonstrations of the rotation of the spheres 
might be found. And he discovered that if, as he puts it, the 
motions of the planets were calculated according to their own 
revolutions, with allowance for the circulatory motion of the 
earth, then the phenomena of each worked out duly. Even more 
important, the orders and sizes of all the celestial bodies, spheres 
and even the heaven itself, were so harmonized that nothing could 
be transposed in any detail without causing confusion throughout 
the universe (Fig. 4). 1 

Copernicus was a theoretical astronomer of genius and origin- 
ality. He must have noted the suspicious reversal of the constants 
of epicycle and deferent between the upper and lower planets: he 
must have perceived the unaccountable intervention of the sun's 
period of revolution in the calculations for each of the five planets. 
Believing that the assumption of an annual motion in the earth 
was no more wild than the assumption of a diurnal revolution, he 
was capable of taking the celestial machinery to pieces and re- 
assembling it in accordance with a different pattern. Working 
from irrefutable observations, he proved that the new pattern 
gave as good results as the old. 

It could hardly give much better results because the parts of the 
machine of the world as revised by Copernicus were essentially 
of the same dimensions as before, though arranged in a different 
order. His determining observations were those of the Greek 
astronomers, Timocharis, Hipparchus, Ptolemy, supplemented by 
the work of their Moslem successors Arzachel, al-Battani and 
Thabit, and his own measurements, few in number and mostly 
made about 1515. Sometimes, as in his determination of the length 
of the sidereal year, his result was less accurate than an earlier 
one (that of Thabit). Copernicus admitted most of the variations 
or anomalies which had been introduced to account for the ap- 
parent changes in some constants (for example, the variation in the 
obliquity of the ecliptic causing an oscillation which was correctly 
explained by Copernicus for the first time; and various com- 
plexities in the motion of the sun, which he transferred, of course, 

1 De Revolutionibus, Preface. The English version in Stimson, op. cit., does not 
always make Copernicus' thought fully intelligible. 


Mercury //brotes on the 
d/am.(380) of the ep/cyc/e 
vftha period of 183 J. 

FJG. 4. The Copernican System of the Universe, (a) General arrangement, 
(b) Lunar theory, (c) The inferior planets, (d) The Earth. The dimensions 
are to scale unless otherwise indicated. (</=days, e~ eccentricity, 
r radius.) 


to the earth). In addition he introduced new elaborations; some, 
like the motion of the apse-line of the earth's orbit already sus- 
pected by al-Battani, were real and necessary, others, like the 
"third motion" of the earth were superfluous or due to the colla- 
tion of inaccurate observations, such as the variation which he 
supposed to occur in the eccentricity of the earth's circle about the 
sun. In fact, mathematically speaking, Copernicus did not create 
a new astronomy in the sense of isolating and measuring every 
celestial motion afresh; what he did do was to reinterpret the 
Ptolemaic structure from the heliocentric point of view, adding 
such refinements as he believed to be necessary. His remark to 
Rheticus, " If only I can be correct to ten minutes of arc, I shall 
be no less elated than Pythagoras is said to have been when he 
discovered the law of the right-angled triangle," shows that his 
ambition in the matter of precision was very limited. And it proved 
in fact that when the first astronomical tables were calculated in 
accordance with the new hypothesis, they were little if at all 
superior to those which had preceded them. 1 

Astronomy remained the doctrine of the sphere, and the imagery 
drawn from it which is so prominent in sixteenth-century imagi- 
native writing was hardly less appropriate to the new theory than 
to the old. Having rejected the prime assumption of cosmology, 
Copernicus had no occasion to challenge others. His geometry of 
the heavens is still that of rolling orbs, save that the earth has re- 
placed the sun in the third sphere. He preserved the fundamental 
division between the sublunary region and the celestial, between 
the natural laws of earth and sky. He insisted even more severely 
than Ptolemy upon the inviolable perfection of circular motion, 
repeated again the proof that the alternative methods of eccentric 
sphere and defercnt-with-epicycle are identical in their results, 
and reduced all motions to combinations of these two forms. The 
reality of the crystalline spheres was unquestioned. Apart from 
his one great innovation, all Copernicus' astronomical thought 
is thoroughly medieval. Truly he reformed the medieval universe, 
because he brought its pattern into a new order, but he introduced 
no new doctrine concerning its composition or the deeper logic of 
its various appearances. 

What, therefore, were the merits of the new astronomical 
system? What arguments could be adduced to show that in this 

1 Cf. Appendix B. 


complicated dance of relative movements the stability of the sun 
was more real than the stability of the earth? Copernicus dealt 
with these two questions as one, but as will be seen they require 
separate answers. In the first place, the pattern of celestial motion 
described by Copernicus and the methods used to work it out in 
detail had several distinct advantages. On the whole, the devices 
were rather more economically displayed, though this is a feature 
whose importance has been exaggerated and, since the observer's 
point of view is geocentric in any case, the geocentric conception 
had some advantages in the ease of handling. The fixed stars were 
fixed indeed, and with the whole system no more than a point in 
comparison with the size of their sphere as Copernicus realized 
from the fact that they revealed no annual parallax the problem 
of predictive astronomy was properly limited to the planetary 
bodies. These now recovered their independence without the 
intervention of any extraneous factor in their revolutions, and the 
main pattern of the planetary mechanisms could now be made 
uniform for all five. Moreover, Copernicus was able to declare, 
for the first time, the relative sizes of the planetary spheres, though 
because he followed Ptolemy's estimate of the earth's distance 
from the sun the whole system was far too small. 1 As the lower 
planets, Venus and Mercury, were now placed between the earth 
and the centre of the universe the peculiarities of their motions 
and their special relation to the sun were explained : clearly they 
could never be observed at a greater distance from it than the 
lengths of the radii of their spheres. The "stations" and retro- 
grade motion of the planets, which had favoured the epicycle 
theory, could now be seen as pure illusions caused by the addition 
and subtraction of the earth's movement and the planets' relative 
to the unchanging background of the starry sphere. The equants 
and uneven revolutions of the Ptolemaic system were removed and 
the principle of perfect circular motion observed more purely. 
Again, the fluctuations in the apparent size of the heavenly bodies 
(as the earth approaches or recedes from them) required by the 
Copernican geometry corresponded more closely to observation 
than those required by the Ptolemaic, particularly in the orbit of 
the moon, which Ptolemy supposed to vary by a factor of nearly 
two. Most of the advantages that can be obtained by supposing 

1 About 5 per cent, of the true value: the dimensions are derived from the 
Ptolemaic planetary constants (see above, p. 1 6) . 


the sun to lie near the centre of all the orbits were actually worked 
out by Copernicus in his calculations, which thus removed some 
redundancies, and threw light on many obscure points. 

On the other hand, it could not logically be claimed that these 
advantages proved the sun to be at rest and the earth moving. 
An interesting variant of the conventional geocentric theory, 
described by Martianus Capella in the fifth century A.D. made the 
lower planets revolve about the sun, and there are references to 
the same idea to prove it was not forgotten in the middle ages. 1 
A natural step beyond this was to suppose all the planets to revolve 
around the sun, while the sun turns about the fixed earth, and it 
was taken by the great Danish practical astronomer Tycho Brahe 
towards the end of the sixteenth century. Mathematically and 
observationally the Tychonic system and the Copernican are 
indistinguishable, in fact the Tychonic is an exact representation 
(in Copernican terms) of what the observer actually sees with 
his instruments. Whatever advantages the Copernican pattern of 
motion had over the Ptolemaic could equally well be claimed for 
Tycho's defence of geocentricity. History has not been kind to 
Tycho's hypothesis, and it has seen (with Galileo) the great 
cosmological debate as being conducted between Ptolemy and 
Copernicus. It is a misleading view. Tycho had enormous 
authority, and his system was quoted as the third possible hypo- 
thesis until late in the seventeenth century. It reconciled the 
combatants without compromising any essential issue; it took all 
that was scientifically sound from Copernicus, and for the rest 
clung to common sense. If we would understand the power of the 
geocentric notion over men's minds we must give it its best 
defence, not its worst, and this Galileo naturally did not do. To 
dismiss Tycho Brahe's contribution as a rather pointless and 
unnecessary obstacle to the advance of truth, or as a conservative 
aberration on the part of the creator of modern positional 
astronomy, is to misrepresent entirely the scientific situation and 
the scientific mind of the sixteenth century. Its importance is 
that Tycho pointed out, with absolute justice, that there was no 
particle of evidence to be derived from astronomy which could 
decide whether the earth moved or not, whereas there was much 
good evidence of another kind to lead one to conclude that the 

1 Heraclides pf Pontus taught this system, with the addition of the diurnal 
rotation of the earth; it is mentioned approvingly by Copernicus. 



earth does not move- Therefore, while the ingenuity of the 
Copernican geometry of the heavens is to be admired, and was in 
fact admired by many who opposed his chief premiss, it must be 
recognized that for the sixteenth century this was irrelevant to 
the main issue, which turned upon different considerations 
concerning the earth's mobility. 

Taken by themselves, and omitting the mathematical improve- 
ments on Ptolemy which are quite neutral in their effect, 
Copernicus' arguments in favour of the moving earth were 
scarcely compelling in their contemporary scientific setting. Nor 
were they very novel. He answered the traditional objections much 
as Orcsme did, developing the thesis that the globe is naturally 
fitted for circular motion. The earth is absolutely round; it is the 
property of a sphere to revolve in a circle, expressing its form in 
its motion; ergo the earth revolves. By this reasoning the movement 
of the earth is natural, not violent: why then should it fly to 
pieces, as Ptolemy supposed? It would rather be much more likely 
that the almost infinitely distant sphere of the fixed stars should 
disrupt under its own velocity, if it were forced to turn round once 
in twenty-four hours, than that the earth should do so. Air and 
water move with the earth, so terrestrial phenomena are unaffected. 
The absence of measurable stellar parallax is explained by the 
immense distance of the stars, and it is argued that it is easier to 
believe that the earth moves, than that the whole heaven moves 
about it. If, as Aristotle seemed to maintain, the condition of rest 
and permanence is more noble and divine than that of change 
and instability, Copernicus replies that rest should in that case be 
attributed to the whole cosmos, and not to the earth alone. In 
discussing the effect of terrestrial motion upon the doctrine of 
gravity and levity, he enunciates an idea of surpassing fertility: 

Gravity is nothing but a certain natural appetite conferred upon the 
parts by the divine providence of the maker of all things, so that they 
should come together in a unity and as a whole in adopting a spheri- 
cal form. It is credible that this property exists even in the Sun, 
Moon, and other planets, ensuring the unchanging sphericity which 
we see, and nonetheless they perform their revolutions in many 

Once more Copernicus has emphasized the fact that the earth is 
of the same kind as the heavenly bodies; and if it is, as he thinks, 
a planet itself, then it must have a progressive circulatory motion 


as well as axial rotation. Finally Copernicus has this glowing 
passage upon the sun: 

In the very centre of all the Sun resides. For who would place this 
lamp in another or better place within this most beautiful temple, 
than where it can illuminate the whole at once? Even so, not inaptly, 
some have called it the light, mind, or the ruler of the universe. Thus 
indeed, as though seated on a throne, the Sun governs the circum- 
gyrating family of planets. 

It is an obvious principle of logic that the unknown cannot be 
demonstrated from the unknown. Measured by this standard, 
Copernicus' arguments in favour of helioccntricity are illogical. 
His aim was to prove that the movement of the earth did not 
conflict with the principles of physics, which of course meant 
Aristotelean physics. But in so doing he interprets these principles 
in a sense different from that of Aristotle, and that understood by 
most of his own contemporaries. He is forced to allege that 
gravity, a tendency to cohere, is a universal attribute of spherical 
bodies. He questions whether rest is inevitable to the elemental 
earth, and motion to the weightless heaven. Contemporaries can 
hardly be blamed if it seemed to them that physics had been 
distorted to fit a newly imagined astronomical theory. Copernicus 
was not a natural philosopher but an applied mathematician, and 
in historical perspective it would have been no weakness in him 
if he had failed to subscribe to contemporary physical notions. 
In the discussion of cosmological systems two possibilities were 
open: either a heliostatic system could be adopted, in which case 
Aristotelean physics was palpably false, and it would be necessary 
to replace it by a new intellectual framework: or alternatively the 
traditional physics might be held to be true, in which case a 
geostatic cosmology was enforced. To attempt, as Copernicus did, 
to reconcile traditional physics and a heliostatic cosmology was to 
choose a course open to fatal criticisms. It was easy enough for 
the opponents of the Copernican hypothesis to show that the 
reconciliation could not be effected, and that its author's justifica- 
tion of it in terms of contemporary doctrine was wholly spurious. 
The new astronomy demanded a new physics; and this was 
ultimately to prove of great advantage to science. But a new 
physics was not Copernicus' creation, and therefore his appeal to 
natural philosophy for tolerance of terrestrial motion was an appeal 
to the unknown; his arguments could carry no conviction because 


they were not derived from the physics in which men believed, 
but to an unsubstantiated adaptation of it. In De Caelo et Mundo 
Aristotle had welded a unity of explanation and, so long as its 
fundamental concepts of motion remained unchanged, this unity 
was not to be broken. 

Ultimately the decision in controversies upon cosmological 
matters which early astronomy was incompetent to decide unaided 
turned upon physical considerations, and here Copernicus, with 
his thoughts still modelled on Aristotle, barely hinted at a new 
approach. Two things make it difficult to view his work dispassion- 
ately. In the sheer majesty of its mathematical achievement De 
Revolutionibus is traditional, but it is a grandly conceived and 
meticulously executed demonstration of the comprehensive powers 
of a new hypothesis. To recalculate every motion and every 
anomaly from the crude observations in accordance with an en- 
tirely original pattern was a task never previously attempted. 
Secondly, it is impossible to escape the compelling power of 
Copernicus' intuition. Like many other original thinkers, he 
uttered the truth for the wrong reasons. His work did not form the 
basis of modern positional astronomy, and within a hundred years 
the doctrine of the spheres no longer played a part in serious 
science; and yet his major premiss was essential to the develop- 
ment of both terrestrial and celestial mechanics. His generalship 
was medieval, but the fruition of his victory lay in the future. 
Lesser men might debate the logic of solar and terrestrial motions 
while an imaginative mind could fasten upon the harmony, the 
irresistible neatness and dexterity of the Copernican pattern. 
Galileo relates that he first relented towards Copernicus when he 
found that the Copernicans were usually well informed in their 
science, in contrast to their opponents who knew only stock argu- 
ments. He read the book and was converted. Men of power and 
vision could learn that the new system, though incapable of 
rigorous proof in detail, contained a transforming conception. 
The constitution of the fertile line of advance at any particular 
moment is not always clear in scientific investigation; Galileo and 
Kepler found it in the Copernican hypothesis. In their work 
Copernicus' intuition that the earth is a planet it can hardly be 
called a reasoned judgement was justified. 

Even a brief survey of the total scientific activity of the sixteenth 
century would require a volume to itself. Here it must be charac- 


terized in a few sentences. (The scientific renaissance caused no 

sudden break in the course ot academic studies, nor did it suddenly 
enable a "scientific method" of investigation to prove its value. 
Most of the problems that were discussed belong clearly in a 
medieval context, and with a few exceptions the procedure and 
style of argument conformed to familiar patterns. Experimental 
science was not born in the sixteenth century. On the other hand, 
the study of pure mathematics flourished exceedingly, and the use 
of mathematical methods in science was successfully extended. 1 
Arithmetics were published in the vernacular languages and print- 
ing also helped to spread and standardize mathematical symbols. 
The Greek geometers were edited and their work thoroughly 
assimilated. Great advances were made in the formulation and 
solution of algebraic equations, and in trigonometry, which in its 
modern form was wholly unknown to the middle ages. The calcu- 
lations involved in astronomy and in practical arts such as naviga- 
tion, cartography, mining, surveying, and " shooting with great 
ordnance," became easily practicable, and books instructing in 
these various forms of applied geometry appeared in considerable 
numbers. When these arts were mathematized, the practitioner 
who had given up rule-of-thumb methods required instruments 
for the measurement of angles and distances, and the rise of an 
instrument-making craft of importance can be traced somewhat 
earlier than the middle of the century. In many places it was 
closely allied with the domestic clock- and watch-manufacture 
which began at about the same time.) 

Opinions concerning the pseudo-sciences, astrology and al- 
chemy, show no remarkable change during the sixteenth century. 
As in earlier times, there were disputes over the merits and sanction 
of judicial astrology, but as the general sentiment was strongly 
favourable there was no sign yet that the dependance of astro- 
nomy on its mother-science was almost concluded. There were 
no sixteenth-century alchemists whose authority stood so high as 
that of the medieval Latin writer Geber, or the early seventeenth- 
century adept who called himself Basil Valentine, 2 but the mystical 

1 D. E. Smith: History of Mathematics (Boston, 1923), vol. I, pp. 292-350. 

2 The former of these was traditionally an Arabic author, but it now seems 
that the works ascribed to him were not composed by the real Jabir (an eighth- 
century physician), though they were put together in Latin from Arabist 
sources, probably in the late thirteenth century. To the latter also a false 
antiquity was traditionally credited. 


attitude to chemical operations was powerfully reinforced by the 
personality of Paracelsus, though he was not an alchemist in the 
conventional sense. Under his influence, strengthened by em- 
pirical discoveries such as that of the specific action of mercury 
against the "new" disease syphilis (first reported c. 1492-1500), 
inorganic chemical remedies were gradually introduced into 
medical practice, against strong opposition from the Galenists. 1 
The use of chemical compounds in medicine stimulated a more 
rational interest in their preparation and properties than that of 
the alchemists, but even more important, perhaps, in promoting 
a purely empirical attitude to material transformations among 
educated men was a new kind of book describing industrial opera- 
tions in a practical manner. Works on smelting and assaying were 
circulating early in the century; the early masterpieces of tech- 
nological description, Biringuccio's Pirotechnia and Agricola's De 
re Metallica, appeared in 1540 and 1556 respectively. Mining and 
mineralogy, smelting and casting, the extraction of saltpetre and 
the manufacture of gunpowder, the making of glass and mineral 
acids, the purification of mercury and the precious metals, were 
here treated in detail, systematically, and from a thorough know- 
ledge of actual practice. Somewhat later similar works on machin- 
ery for lifting, pumping, sawing, textile manufacture etc., in a 
slightly less realistic vein, likewise did much to place engineering 
on a sound basis of description. 

In medicine, it is probable that the education of physicians and 
surgeons improved considerably, owing to the new accessibility 
of the Greek authorities, and to the new anatomical tradition 
founded by Vesalius and his contemporaries. There were many 
serious problems: war, which has always stimulated the progress 
of surgery, presented the new horror of gunshot wounds, and the 
rapid growth of towns favoured the spread of disease. Public 
health was less a matter of public concern in the sixteenth-century 
city and state than it had been in the medieval. While, broadly 
speaking, there was no great revolution in the theory and practice 
of medicine, there were many advances in detail. Jesuit's bark 
introduced from Peru contained quinine as a specific against the 
recurring fever of malaria. The pharmacopoeia was standardized 

1 The origin of syphilis has been exhaustively investigated. Recent opinion 
seems to be against the view that it was introduced into Europe from the 


first in Italy and Germany, not in England until the London 
Pharmacopoeia was issued in 1618. Most dramatic of all perhaps 
was the influence of the French surgeon, Ambroise Pare, who led 
the way in abandoning the use of the fiery cautery, previously 
applied to all gunshot wounds (which were believed to be en- 
venomed) as well as in cases of amputation. Although Pare still 
modelled his practice broadly on that of the Ckirurgia of his great 
fourteenth-century countryman, Guy de Chauliac, (which was 
itself often reprinted in the sixteenth century) his writings did 
much to raise the prestige and skill of the surgeon. Guy, who 
himself leaned heavily upon Galen and Avicenna, had taught 
that the ' surgeon who is ignorant of anatomy carves the human 
body as a blind man carves wood,' and Pare reinforced this 
truth by making free use of Vesalius' De Fabrica. 

The sixteenth century also saw the current of realism at work 
in natural history. Of this something more must be said later 
(Chapter X). The best work was still compilatory, and encyclo- 
paedic on the vastest scale. It was devoted entirely to the superficial 
characteristics and habits of plants and animals, and botany 
remained an adjunct of medicine rather than a discipline in its 
own right, but much rubbish was purged from the medieval garner 
of fact and legend. The humanistic naturalists used a scissors-and- 
paste technique upon the authentic texts of Aristotle or Pliny, 
and if the range of their reading and collation was wide and 
discursive, some of them show for the first time a real eye for 
genuine observation, and painstaking endeavour to confirm at 
least the external features of their subjects. The first monographs 
in natural history have an authentic realism and attention to 
specific detail which are entirely new. 

On the whole, however, the scientific spirit of the century 
developed naturally from the work and progress of the later middle 
ages. A hasty reference to the output of the printing-press may 
act as a guide to the nature of contemporary taste and estimations; 
the most sought after and respected books were still those com- 
posed long before the invention of printing. 1 Neither the library, 
nor the academic training, of the medieval world were suddenly 
outmoded by a vast efflux of novel aspirations and methods. The 
mythical " renaissance man" of the early sixteenth century, 
though his tastes might be more hedonistic than those of his 

1 See Appendix C. 


forefathers, though he might be more enamoured of the powers 
and potentialities of this world and less regardful of the next, was 
still largely limited in his science to the achievements of the 
medieval renaissance: his very classicism only attached him more 
deeply to the same roots of western learning. The cosmos of 
Shakespeare is the cosmos of Dante, save that the former was a far 
less philosophical poet: the Fables of Bartholomew, the complex 
vocabulary of astrology and alchemy, and the doctrine of the four 
humours still enclosed the framework of science which most men 
knew. It was not the experimentally minded Dr. William Gilbert, 
with his glass rods, magnetic needles and other trivia, who was 
most honoured at the court of Elizabeth, but Dr. John Dee, the 
astrologer and magus, holding, as it seemed, the keys to far graver 


UNTIL the end of the sixteenth century scientific innovations 
were put forward with deference and almost a sense of 
humility. A great deal of the best work of this period was 
entirely non-polemical: to this class belong the first stages of the 
Vesalian tradition in anatomy, and much purely descriptive 
writing on natural history, mineralogy and chemistry. The works 
of Agricola or Rondelet were excellent contributions to science 
as positive knowledge, but they created no ferment of new ideas. 
It is true that Paracelsus is supposed to have burnt the books of the 
masters before his inaugural lecture at Basel in 1527, and that he 
declaimed against official medicine: 

I will not defend my monarchy with empty talk but with arcana. And 
I do not take my medicines from the apothecaries. Their shops are 
but foul kitchens from, which comes nothing but foul broths. . . . 
Every little hair on my neck knows more than you and all your 
scribes, and my shoebuckles are more learned than your Galen and 
Avicenna, and my beard has more experience than all your high 
colleagues. 1 

Paracelsus, whatever his other merits, was a picturesque ranter 
and it is futile to portray him as a herald of the scientific revolu- 
tion. The texture of his thought in which it is difficult to see any 
precise pattern was woven upon a mystical conception of nature 
entirely alien to that of natural science. 2 Medicine was indeed 
torn by faction: the Arabists and the Humanists, the Paracelsians 
and the anti-Paracelsians, the cauterizers and the non-cauterizers 
sharpened their wits in vituperative debate as they contended 

1 Paracelsus: Selected Writings (edited with an introduction by Jolande 
Jacobi), (London, 1951), p. 79. 

2 As, for instance, the perennial fallacy that the virtues of herbs are indi- 
cated by their structure. * Behold the Satyrian root, is it not formed like the 
male organs? Accordingly magic discovered it and revealed that it can restore 
a man's virility. . . . And then we have the thistle: do not its leaves prick like 
needles? Thanks to this sign, the art of magic discovered that there is no better 
herb against internal pricking . . .' etc. (ibid., p. 186). 



for supremacy within the profession, without aiding the advance- 
ment of knowledge. Natural philosophy and natural history were 
not similarly divided by quarrels arousing professional passion, 
though inevitably personal jealousies were not lacking. More 
typical of the relations between old and new were Copernicus 
taking leave to speculate afresh on the revolving spheres, Vesalius 
adapting his text to follow Galen. As yet, content if they could 
show that new ideas were no worse than old ones, men were far 
from asserting that the House of Learning was a crazy, rambling 
warren that needed to be pulled down and reconstructed. With 
the exception of Paracelsus, no scandalous defiance of authority 
had been noised abroad; and this was partly because the shape of 
authority, the policy and content of conservatism, were themselves 
unsettled at this nascent stage of modern science. 

When the famous crisis was reached in 161516, it had already 
been foreshadowed in the tragedy of Giordano Bruno's life which 
must be mentioned in its proper place. Bruno was no scientist, 
and his impact, his historical importance, his ultimate influence 
upon the development of non-scientific attitudes to science, were 
all the more startling for that reason. It must not be imagined 
that the ways of the ordinary, common-sensible religious man and 
of the critical natural scientist were bound to deviate at the first 
novelty, or that the sixteenth century was afflicted by the same 
opposition of loyalties and criteria of truth that troubled the 
nineteenth. On the contrary, every flaw in the conventional 
account of nature was examined not in the hope that it would 
profit one philosophy against another, but in the belief that its 
examination would advance truth, and that in truth all matters 
of importance were ultimately reconcilable. The view that a 
man's access to truth might be measured by the nature of his 
ideas on celestial mathematics was not known to the sixteenth 
century. Copernicus' narrow vision had embraced no more than 
the validity of a single hypothesis: it was with the wider philo- 
sophical perspective of Bruno, and the wider scientific range of 
Galileo, that iconoclasm assumed a massive, threatening character. 
Disputes among mathematicians, astrologers or physicians could 
be tolerated (these things were not suddenly born at the time of 
the renaissance) but criticisms shaking the roots of philosophy 
had to be repelled. It was not simply a question of the liaison 
between Aristotle and religious doctrine, nor was Catholicism the 


only opponent of innovation. 1 The new scientific philosophy of 
the early seventeenth century, speaking with a confident voice 
that demanded credence, met sheer mental inertia and the weight 
of academic omniscience. Men resent admitting that they have 
given their lives blindly to the defence of absurdities, and it was a 
new generation, not similarly committed, that devoted itself to 
the prosecution of Galilean science. 

Galileo's greatest fame is as an astronomer, yet in intellectual 
quality and weight his one treatise on mechanics almost outweighs 
all the rest of his writings. Although his book on cosmology 
became notorious, and had a more general public influence, it 
had no comparable effect upon the future development of scientific 
astronomy, for its polemics were suited only to its own age. The 
contradiction here is more apparent than genuine. Though 
formally divided between two branches, Galileo's creative activity 
in science was a unity, not twofold: it was a unity in laying down 
revised principles of procedure in science, and again in its specific 
exemplification of these principles, since Galileo saw that the 
science of motion and the just appraisal of the results of observa- 
tional astronomy were the twin keys to an understanding of the 
universe. This is not to say that his comparatively minor (though 
in themselves major) researches, into thermometry, the properties 
of pendulums, the grinding of lenses, the strength of materials, 
the theory of the tides or the measurement of longitude at sea were 
not conducted with the same zest for knowledge, or that they were 
either irrelevant or auxiliary to his main achievement. Each one 
of his minor discoveries would have been notable in a lesser man. 
Each has its important place close to the origins of modern 
physical science. But Galileo's physical experimentation, like his 
turning of the telescope to the heavens, was original and fecund 
only in the sense that it was initiatory. Other men took up his 
experiments, and even drew more valuable conclusions from them 
than Galileo had done, by following and expanding his methods; 
and while the initiation of a new kind of scientific activity is itself 
an achievement of the first order, it is not of the same dignity 
as the induction of fundamental principles which henceforth 

1 In the first half of the seventeenth century the " new philosophy" advanced 
most rapidly in two Catholic countries, Italy and France. Criticism of its 
principal tenets was no less forceful among Protestants (e.g. Francis Bacon). 
Cartesian science was very rapidly adopted by men of orthodox religion in 


dominate a whole field of science. Besides fulfilling this function 
in dynamics, Galileo demonstrated the connection between its 
principles, when properly understood, and the disputed points of 

Unlike his predecessors Galileo consciously assumed the attitude 
of a publicist and a partisan. Writing more often in his native 
language than in Latin (for Galileo was one of those who led the 
way in abandoning for science the official language of philosophy), 
he shaped his arguments to a broad audience. His dialogues were 
lively, his irony biting, and he did not scruple to make a merely 
debating point. Zealously he magnified the weaknesses of con- 
ventional science in order to turn it to ridicule. Almost alone 
among the ancients the experimenter and mathematician 
Archimedes was singled out for Galileo's commendation; Aristotle 
he treated almost as an ignoramus, as though the subtlety and 
intricacy of that intellect, preventing vision of the simple truth, 
had composed fantastic webs of improbability and artificiality. 
He had no doubt at all that the modern way was infinitely superior 
to the ancient, and hardly mentioned any contention of the 
Peripatetics that he was not prepared to deny. This habit of 
opposing conventional ideas was not, apparently, a product of 
Galileo's maturity nor of his great discoveries. Rather the critical 
attitude which stands out even in his juvenilia was the source of 
his original ideas. Born in 1564, by 1589 Galileo was already a 
teaching member of the University of Pisa, where he attracted 
the attention of the Grand Duke of Tuscany. Two of the most 
famous stories belong to these Pisan years: here he observed the 
equality in time of the swinging cathedral lamps, and carried out 
(as his first biographer relates) the famous experiment of dropping 
weights from the Leaning Tower. 1 Unlike most academics of the 
time, Galileo remained a layman. The resentment aroused among 
his colleagues by his criticisms of Aristotle prompted his removal 
in 1592 to Padua, within the anti-clerical Venetian state, where 
there was a long tradition of freedom in scientific thought and 
where anti-scholastic opinions, if not exactly encouraged, were 
at least tolerated. At Padua Galileo studied mechanics, constructed 

1 The experiment from the Leaning Tower, told in glorification of his 
master by Viviani, has been rejected by many scholars as lacking support in 
contemporary documents. At any rate Galileo was not the first to subject 
Aristotle's dynamics to this particular test. 


his first telescope, and began his long battle on behalf of the 
Copernican system. After his growing fame had brought about his 
recall to Florence, under the special patronage of the Grand Duke 
and with an appointment at Pisa (1610), Galileo was particularly 
warned to avoid utterances having a theological implication. 
From 1609 to 1633 he was immersed in his astronomical observa- 
tions and the polemics they provoked; then after the publication 
of the Dialogues on the Two Chief Systems of the World (1632) there 
followed his trial and recantation: yet having been condemned to 
silence, Galileo published his greatest work at Leiden in 1638. 
The significance of his summons to Rome is easily exaggerated. 
Galileo did not compel the Roman Church to condemn Coper- 
nican astronomy: this intervention in scientific discussion had 
already taken place decisively with the decree of 1616, and was a 
natural consequence of the condemnation of Bruno. The only 
interest in the trial concerns the nature of the judicial process, 
which is not impeccably transparent; but though Galileo may 
not have broken a private pledge, he had certainly contravened 
a general order. 1 Good Catholics were placed in a false position 
for two centuries by the decree and Galileo's trial under it, without 
these preventing excellent work in practical astronomy in Italy, 
or the uninhibited development of other new studies there. Even 
the Copernican Alfonso Borrelli was able to make his suggestive 
contribution to celestial mechanics (1660) by means of an 
ingenious quibble. 2 

A reading of the Mathematical Discourses and Demonstrations 
concerning Two New Sciences (1638) does not, however, give a true 
picture of the revolution in dynamics as Galileo effected it, any 
more than the earlier series of Dialogues can now be considered 
as a balanced statement of the respective merits of the two 
cosmologies. In his book Galileo the polemicist is in full cry after 
the absurdities of Aristotelean physics, but in fact it is very 

1 However obvious this may now seem, it was not so to the ecclesiastical 
censors who affixed the imprimatur to the Dialogues in 1632. 

2 The decree distinguished between the annual revolution of the earth, 
* utterly heretical because contrary to Holy Scripture,' and the diurnal 
rotation, * philosophically foolish.' One of its more curious results, as I learn 
from Dr. Joseph Needham, was that Chinese astronomers, being instructed by 
Jesuit missionaries, remained ignorant of the Gopernican theory until the late 
eighteenth century. Borelli observed its letter by overtly limiting to Jupiter 
and its satellites a discussion of planetary motions which he obviously intended 
to apply to the earth and moon. 


likely that Galileo was never an Aristotelean physicist in the true 
sense, and that the original account of motion was never urged 
upon him as a true and satisfactory explanation. Much patient 
scholarship has been devoted to the origins and development of 
Galileo's mechanics; at one stage it seemed as though its godfather 
was Leonardo da Vinci, until it was found that Leonardo was 
only re-echoing a current of medieval thought. At first these 
medieval discussions were regarded as no more than imperfect 
gropings at a truth which Galileo apprehended perfectly. Today 
the theory of impetus appears as a theory of motion in its own 
right, not an uncertain anticipation of Galileo, but a coherent 
doctrine which provided Galileo with a firm starting-point. The 
theory of impetus could not develop the modern conceptions of 
inertia and acceleration by a smooth process of transition and 
expansion, but it did provide a more convenient, and more 
adaptable, starting point than the ideas expressed in Aristotle's 
Physics. Galileo's achievements are more properly measured by 
comparing his own science of dynamics not with the absurdities 
he discovered in Aristotle, but with the theory of impetus which 
was already well formed. 

Since it had been handled by Oresme in the fourteenth century 
this theory had made little progress up to the time of Galileo. 
Remaining a somewhat specialist complexity, it had not sunk to 
the popular level of exposition, but it was taught by respectable 
mathematicians and philosophers, including Cardano (1501-76), 
Tartaglia, Benedetti and Bonamico who was Galileo's own 
master. Tartaglia (1500-57), moreover, succeeded in making a 
useful application of the impetus theory to ballistics, and was the 
first writer to aim at computing the ranges of cannon by means of 
tables derived from a dynamical theory, in which task Galileo 
later was to believe himself successful. After Tartaglia, if not 
before, it was at least clear that in this particular respect a 
dynamical theory ought to be quantitative, that is it should be 
capable of making exact numerical predictions. Many writers 
on gunnery, with varying degrees of imagination, continued to 
search for this desideratum within the framework of the impetus 
theory until well after Galileo had offered a far better one. This 
essential sterility of the impetus theory in the sixteenth century is 
an important point. Able men failed to derive from it a mathe- 
matical description of the phenomena of motion, yet failed also 


to develop concepts which could take its place. It is not, therefore, 
the case either that Galileo's ambition to mathematize dynamics 
was something unusual in the contemporary scientific milieu, or 
that, once this ambition had been framed, it was easy to mould 
the necessary modern dynamical concepts out of their crude 
impetus forebears. Modern dynamics did not spring from a 
modified version of the impetus theory: Galileo was compelled to 
return once more to the fundamental concepts of motion. 

Towards a new Kinematics 

The theory of impetus, the living tradition of dynamics in the 
sixteenth century, utilized by Galileo himself in his early treatise 
On Motion (1592), had the basic function of explaining certain 
phenomena. It had not changed the language in which they were 
described. While it gave reasons for the continuation of motion by 
a body after the moving agent was withdrawn, and in particular 
accounted for the properties of motion shown by falling bodies 
and projectiles, it had not produced more accurate or fertile 
definitions of force, velocity, acceleration. In the technical terms 
of philosophy it dealt with the " accidents" of motion the 
decelerating ascent of a projectile was caused by an "accidental 
levity," its accelerating descent by an "accidental gravity," 
demonstrated by its having effects on impact equal to those 
caused by a body at rest of much greater weight. Impetus as a 
causal factor, responsible for the accidents of free motion, being 
thus associated with the categories of Aristotelean dynamics, no 
mechanician before Galileo attempted to deny the validity of the 
substantial distinction between the two kinds of motion, natural 
and violent. Hence great difficulties arose when the attempt was 
made to describe the path of a projectile, for example, since the 
two parts of the problem the ascent and the descent were 
qualitatively distinct and subject to different considerations. 
Further, progress towards a kinematics through this type of 
problem was obstructed by the limitation of the impetus theory 
to strictly rectilinear motion. Though both Leonardo and 
Tartaglia in the sixteenth century represented the trajectory of a 
projectile as a continuous curve, this was no more than a pictorial 
device, since their common theory of motion allowed no com- 
pounding of natural and violent. In theory the categories of 


motion were exclusive, and rectilinear-natural motion could only 
occur after the rectilinear-violent was completed. Again, if the 
relations between the impetus theory and the later concept of 
inertia are examined, it is clear that while in isolated statements 
exponents of this theory seem to anticipate the rigorous definition 
of inertia, in the full physical context their interpretation of the 
phenomena was different. For it was not supposed that a body, 
having acquired an impetus to motion, would continue to move 
at a uniform velocity. The resistance of the medium ensured that 
it would slow down and come to rest; and motion in a vacuous 
space was inconceivable when the universe was regarded as a 
plenum. Impetus was like heat, an evanescent accident of matter, 
of its own nature wasting away. As before, thought on the appli- 
cation of these ideas to the special problem of projectiles was 
misled by utter deficiency of observation and description. The 
impetus mechanicians universally believed that the velocity of a 
projectile increased for a space after it had parted company with 
the propellant, so that in some strange way its impetus was 
actually increased during a part of its free motion. Here also the 
theory, instead of leading to universally valid concepts of inertia 
and acceleration, required the formation of a special case. 

If the scientific tradition inherited by Galileo did not offer any 
simple, universal axioms in dynamics, and in its preoccupation 
with causation had neglected accuracy in description, it did 
provide a suitable mathematical analysis for dealing with changing 
quantities, such as the velocity of an accelerated body. It is a 
matter of historical record that the geometrization of motion, the 
establishment of a formula connecting velocity, time and distance 
appropriate to the motion of an accelerated body such as a freely 
falling mass, was more easily accomplished than the development 
of a framework of kinematics within which such a formula would 
be not merely possible but inevitable; the formulation of a true 
dynamics involved a still greater effort which was hardly com- 
pleted before the eighteenth century. The effect of supposing a 
uniform (linear) variation in the intensity of a quality, such as 
heat, had been studied by a number of philosophers in the 
fourteenth century. They found that the second variable (e.g. 
heat) could be related either arithmetically or geometrically to 
the first variable (e.g. time). Oresme, for example, had demon- 
strated that if a quality be supposed to vary uniformly from the 


magnitude represented by the line AB to zero at C (Fig. 5), the first 
variable being represented by the line AC, this varying quality is 
equal in effect to a uniform quality of 
the magnitude AB, since the area of 
the triangle ABC is equal to |AB.AC. 
He expressly stated that if the varying 
quality were velocity, the equivalent 
uniform velocity would be that 

attained at the mid-point in time (i.e., ^ < . 

if AC represents time, of magnitude Fm 5 Geometrical analysis of 
|AB) and deduced that any uniformly uniformly varying qualities, 
varying quality (or velocity) could be 

equated to a uniform quality (or velocity). Somewhat earlier 
another master of the University of Paris, Albert of Saxony, had 
tried to prove that the motion of a freely falling body could be 
treated in this way; he had taught that (i) such a body is uniformly 
accelerated, and (ii) that in uniform acceleration the instantaneous 
velocity is directly proportional to a first variable which is either 
the time elapsed or the distance traversed. 

The first of these propositions was supported, from Albert's 
time to that of Galileo, by reference to the theory of impetus. It 
was asserted that the continually increasing speed of a falling 
body was caused by the addition, to the impetus already acquired 
by it at any point in its descent, of the constant tendency (conatus) 
towards the attainment of its natural place which it always 
possessed. If this conatus were suddenly abolished while the body 
was actually falling, its impetus would nevertheless bring it down 
to the ground at a nearly constant speed, but as this conatus acted 
as a cause of motion on a body already in motion, it made it move 
ever faster. By an intuitive process, rather than by strict reasoning, 
it was argued that the increase of velocity is linear; 1 an argu- 
ment not approved by all philosophers. It was not accepted by 
Galileo in 1592, for it might be that the rate of increase would 
slacken as the falling body moved more quickly. 

The second proposition, or rather pair of alternative proposi- 
tions, involved even more obvious difficulties. In the first place, 

1 Intuitive, because Albert's proposition really implies the true law of 
inertia, which he did not enunciate, and also because it is untrue when the 
descent occurs in a resisting medium, such as the air. Nor was it logically 
certain that the conatus would act in the same way on a body in motion, as on 
one at rest. 



the notion of instantaneous velocity was very imperfectly grasped 
no term existed to describe it for while the calculus of varying 
qualities could equate these, over a given range, with uniform 
qualities, it did not deal with the instantaneous magnitude of the 
changing quantity. Moreover even problems on simple linear 
relations involve integration, and it was by no means easy to 
decide what the integral (the area ABC in Oresme's demonstra- 
tion) actually represented. To Oresme it was the total quantity 
of a quality over a given range, expressed as a simple product 
(p x q) ; but whereas this meaning could be applied to a quality 
such as heat, it was hardly applicable to velocity. 1 What is the 
"total quantity of a velocity"? In either version of Albert's 
second proposition, when the calculus of varying qualities was 
applied, this mysterious quantity appeared, but the three useful 
terms time, velocity and distance could not be brought to 
appear together. The difficulty can be explained, of course, in 
modern terms by realizing that the product (\vt) or (\vs) cannot 
possibly represent any "quantity of velocity." Galileo was the 
first to demonstrate this, by showing that the integral is a measure 
of the distance traversed. There was no question here of a purely 
mathematical difficulty Galileo's geometry is exactly that of 
Oresme he succeeded by attaching correct conceptual signifi- 
cance to the mathematical quantities. 2 Thus his originality was 
not so much in making a particular calculation, as in interpreting 
the answer once he had obtained it. 

Finally, the philosophers who followed Albert had to decide 
between the alternatives in his second proposition. Was the first 
variable time or distance? This was the principal obstacle to 
progress in the sixteenth century within the framework of the 
impetus theory. And it was so, not because a choice could not be 
made, but because it was not even clear that a choice was neces- 
sary. Leonardo typified the confusion of thought in his completely 

1 This assumes, for example, that a hot iron having a temperature t t falling 
to / 2 over time T melts as much ice in that time as an identical iron of constant 
temperature J(^ -f- J 2 ). It was only much later that Black cleared up the 
confusion between temperature and quantity of heat, analogous to the con- 
fusion in mechanics here discussed. 

2 His geometry was equivalent to the derivation of the integral (^at z ) from 

the differential equation . == at. He realized, correctly, that this represented 
the distance traversed. 


clear, and completely contradictory, statements in different 
passages of his note-books that the velocity of a falling body at 
any instant is proportional to the distance fallen, and to the time 
elapsed. For the writers on kinematics who preceded Galileo, 
what he was to call the supreme affinity between time and motion 
was inevitably obscured. They could not measure small time- 
intervals. They most naturally stated the problem whose solution 
they sought in a form which made time a function of distance, 
that is: "If a stone falls x feet in one second, how long will it take 
to fall 100 feet?" Even in making experiments on dropping 
bodies from different heights, it was more natural to think of 
the greater velocity as a function of the greater elevation. It 
seemed that the lifting of the stone to a greater height was the 
direct cause of its greater velocity on reaching the ground. This 
confusion of hypotheses was indeed to trouble Galileo himself, 
and some of his brilliant contemporaries. Only one philosopher of 
the sixteenth century steered his way unambiguously through it. 
This was a Spanish theologian, Dominico Soto, whose commentary 
on Aristotle's Physics, fully in the tradition of Oresmc and Albert 
of Saxony, was published in 1545. After defining "uniform 
difForm" motion (i.e. uniformly accelerated motion) not 
velocity as proportional to time, he declared that this kind of 
motion was proper to freely falling bodies and to projectiles. 1 He 
did not, however, prove these propositions nor did he suggest a 
formula relating time, velocity and distance. 2 Though he gave 
the definition and application of acceleration correctly, he was 
still far from a true kinematics, and his propositions were still 
dubiously derived from the concept of impetus. If they were 
significant, but limited, anticipations of Galileo's theories on 
motion, they were also nothing more than one version of Albert 
of Saxony's propositions. And there was no further advance. It 
was left to Galileo to perform two functions of highest importance: 
to formulate new, clear concepts of motion, and to derive from 
them the complete elements of kinematics, using the fragments 
provided by those who had shaped his intellectual inheritance. 

1 Cf. P. Duhem: fitudes sur Leonard de Vinci (Paris, 1906-13), vol. Ill, 
pp. 267-95, 555~ 6 2- 

2 i.e., though Soto loosely gives the equivalent of , = at, he did not attempt 

to integrate this equation. As will be seen, this was a task that defeated Des- 
cartes, and (at first) Galileo. 


The Law of Acceleration 

During more than two centuries before Galileo's birth the 
application of the calculus of varying qualities to the concept of 
impetus promised the discovery of the law of acceleration or 
rather of two such laws. 1 Dominico Soto had decided correctly 
that acceleration was a rate of change of motion (velocity) in 
time. He had even struck a blow at the dichotomy of natural and 
violent motion by deducing that in the violent motion of ascent 
the acceleration is negative. Although Galileo's great achievement 
was to be in the mathematical analysis of motion, it was not his 
first preoccupation. Instead, in his treatise On Motion of 1592, he 
examined the physical nature of acceleration, and criticized the 
opinions commonly derived from the concept of impetus. In the 
physical sense, he maintained, acceleration was a mere illusion. 
His argument at this stage denied the proposition which became 
one of the axioms of modern dynamics a constant force gives a 
body a constant acceleration for he argued that since the cause 
of the natural motion of a body is its weight, each must have a 
natural velocity proportional to its weight. He explained the 
appearance of changing speed in this way: suppose a heavy mass 
projected upwards, the impetus conferred being greater than the 
natural conatus to descend. It will rise until the tendency to fall 
and the impetus are of equal strength. At this point the body still 
possesses a certain degree of impetus and consequently as it begins 
to fall back it will increase its speed until all the impetus has 
disappeared; after this its motion will have the constant velocity 
proper to its weight. In the case of a body falling from rest, he 
declared, the impetus acquired by its displacement from the 
centre was preserved and the same explanation held. 2 

Certainly this novel modification of impetus mechanics one 
enforced by allowing notions of the causal functions of impetus to 
prevail over its usefulness in kinematics introduced no remark- 
able clarity. It may be that Galileo's somewhat unfruitful specula- 
tions along these lines had the effect of turning his thoughts in 

1 The law relating instantaneous velocity to distance traversed (-T = as) 

makes s an exponential function. It was therefore beyond the mathematical 
competence of Galileo's age. 

2 This theory is discussed in detail by A. Koyre: Etudes Galiltennes (Paris, 
1939). PP- 


a new direction. The followers of Oresme and Albert had long 
abandoned the idea that the speed of a falling body is proportional 
to its natural weight, though they did not conclude, as did Galileo 
later, that in a vacuum all bodies would fall at the same velocity. 
Oresme, for example, opposing Aristotle, held that the uniform 
velocity of a body is not proportional directly to the "puissance" 
applied (e.g. its weight), but to the ratio between the "puissance" 
and the resistance to be overcome. He recognized also that the 
natural weight of a body is unaffected by its motion; the only 
change is in apparent or effective weight, and it is to this (at any 
instant) that the velocity is proportional. 1 Moreover, Oresme 
accepted the fact that acceleration may continue indefinitely, 
and thus differed in principle from Galileo who assumed in 1592 
that the velocity of a falling body tends towards a uniform value. 2 
But it is true that the identification of impetus with accidental 
gravity involved conceptual inconveniences which Galileo had 
correctly appreciated, though he set them into an outmoded 
Aristotelean pattern. 

The first evidence of a major success already shows that Galileo 
had turned from a physical-causal to a kinematical approach. In 
1604 he wrote, in a famous letter to Paolo Sarpi, that on the basis 
of an axiom sufficiently obvious and natural he had proved that 
the spaces passed over by a falling body are as the squares of the 
times. The axiom adopted was that the instantaneous velocity is 
proportional to the distance traversed; an axiom already rejected 
by Dominico Soto. The demonstration of this impossible con- 
clusion (which happens to survive) 3 made use of the medieval 
calculus of varying qualities. Galileo decided that the integral 
(area ABC in Fig. 5, Oresme's "quantity of velocity") represented 
the space traversed; but the process by which he derived this 
integral from his axiomatic function was entirely false. His 
reasoning assumed, in fact, that velocity was plotted against time, 
not against distance. 4 Thus the familiar theorem, s = %at 2 , was 
first derived by Galileo in a process mathematically correct but 
vitiated by a conceptual error. Perhaps the theorem was first 
tested about this time by the experiment of rolling a brass ball 

1 Oresme, Medieval Studies, vol. Ill, pp. 230-1; vol. V, pp. 179-80. 
a In the Discourses Galileo explains that the resistance of the air tends to 
limit the velocity of a falling body to a maximum value. 

3 Gf. Opere (Edizione Nazionale), vol. VIII, p. 373. 

4 Duhem: Etudes sur Leonard de Vinci y vol. Ill, pp. 565-6; Koyr6, op. cit., p. 98. 


down an inclined plane described in the Discourses* It is certain, 
at least, that from this time Galileo was convinced of its accuracy 
as a mathematical description of the motion of freely falling bodies. 

In Galileo's scientific method experiments were designed to 
give ocular confirmation of reasoning; therefore he could not be 
satisfied with his newly discovered theorem as a merely empirical 
fact. At this point he was most concerned to prove that his axiom 
the false law of acceleration followed logically from an analysis 
of the nature of motion, and to establish it as a reasoned premiss. 2 
Could it be justified in philosophy? In tackling this question he 
must have been aided by the progress of his thought since 1592, 
of which unfortunately little is known. Probably he had already 
gone far in renouncing that concern for the causation of pheno- 
mena shown in his early writing after realizing the confusion into 
which it plunged dynamics. In the later phases of his thought 
impetus was no longer appealed to as a causal factor but became 
a mathematical quantity the product of weight and velocity. As 
Galileo's problem became more purely kinematical, he accepted 
the facts of gravitation and the fall of heavy bodies without 
trying to impose an explanation, although, from his favourable 
references to William Gilbert after 1600, it may be presumed that 
he approved the notion of gravity as a quasi-magnetic attraction. 3 
Already in 1604 he saw acceleration as a fact to be defined, not 
explained; but it was not until afterwards that he was satisfied 
that the constant effect produced by the constant cause, a force, 
is not a velocity but a rate of change of velocity and so resolved 
the paradox he had treated very differently in 1592. 

With the abandonment of the impetus causation of acceleration 
is involved the transformation of this vague conception into the 
law of inertia. Mach insisted, logically, that this law is the special 
case of the law of acceleration where the force applied is nil, and 
therefore no separate statement of it is strictly necessary. 4 His 
argument is just, but not historical. Historically the special case 
was more readily understood than the general law. It was derived 

1 Dialogues concerning Two New Sciences, trans, by H. Crew and A. de Salvio 
(New York, 19 14), pp. 178-9. 

2 The empiricist would have derived the law of acceleration mathematically 
from the law of distances verified by experiment; but this was not Galileo's 

3 Dialogues on the Two Chief Systems of the World, pp. 426 et seq, 

4 Ernst Mach: Science of Mechanics (Chicago, 1907), pp. 142-3. 


from the consideration of motion in a resisting medium: if the 
impetus of a body is expended in overcoming the resistance, then 
in the absence of resistance its impetus and velocity will remain 
infinitely constant. It is in this way that Galileo explains the law 
of inertia in his Discourses, and the non-resisted motion of the 
celestial spheres had long been described as a peculiar instance of 
undiminished impetus, or inertial rotation. The gcometrization of 
space, the transference of the phenomena of motion from the real 
world of resisting media to an imaginary vacuous space (in which 
Galileo had been partially anticipated by Benedetti) and the 
restriction of impetus to a kinematic sense virtually necessitated 
the transformation of the traditional idea of continued motion 
into the idea of inertia, which marks the complete downfall of the 
ancient attitude that it is motion, and not rest, which requires 
particular explanation in face of the modern notion that only 
changes of motion require explanation. In Oresme's natural 
philosophy impetus, the motive virtue, had been inevitably a 
failing "puissance"; Galilean kinematics required that inertial 
motion be uniform because the reason for its retardation had been 
removed. The statement of the law of inertia was indeed fore- 
shadowed in the treatise On Motion, where Galileo discussed the 
motion of a sphere rolling on an infinite horizontal plane, a 
motion which is neither violent nor natural and therefore can be 
the result of the action of an infinitely small force; or where he 
showed that from the abolition of resistance, as in a vacuum, it 
did not follow that movement would be infinitely swift. And if, 
in such inertial motion, the causal-impetus was conserved, what 
could be its function when there was no longer a resistance to 
overcome? At this point the conservation of impetus became 
redundant: it was only necessary to speak of the conservation of 
velocity and momentum. 1 

Once the vague concept of impetus had been analysed into two 
rigorous statements embodying the law of inertia and a defini- 
tion of momentum, the potentialities of the geometric method in 
kinematics were vastly extended. With the further addition of an 
arbitrary law of acceleration the fundamental theoretical structure 
of kinematics was almost complete, and at once the distinction 
between "natural" and "violent" motion appeared as an unneces- 
sary hindrance. The terms were still used by Galileo, but purely 
1 Koyre, op. cit., pp. 71, 93. 


for classification, without any causal or dynamical significance. 
Natural motion had become, by definition, accelerated motion 
in accordance with the normal law: the violent, a motion retarded 
in accordance with the same law of opposite sign. Gravitation had 
become a force like any other, which might be greater or less than 
other forces opposed to it, and the effect of a force was to accelerate 
or retard a body whose only physical properties were weight 
(which Newton made, more properly, mass) and inertia. Privi- 
leged directions with respect to the centre of the universe, intrinsic 
lightness and heaviness, causal distinctions between enforced and 
unenforced movements, all disappeared once the aptitude of the 
law of inertia in perfectly geometrical vacuous space, where all 
planes are infinite, all perpendiculars are parallel, and only simple 
forces operate, was realized. 

It need not be supposed that Galileo had, by 1604, reached the 
stage where the distinction between the essence and the accidents 
of motion for which he had sought so long, and which was essential 
for the elucidation of the true laws of kinematics, was perfectly 
clear in his thought. Rather, his erroneous definition of accelera- 
tion at that time, together with the imperfect conception of 
inertia which he was never to amend, prove that the steps in the 
process of reasoning he had followed still lacked clarity and 
rigour. Having abandoned the traditional theory of impetus 
Galileo's intuition had brought the laws of kinematics almost 
within his grasp, at a time when his analysis of the nature of motion 
was still far from impeccable. The more adequate reasoning of 
the Discourses was to be developed over the next thirty years, yet 
even so the ultimate confutation of the false law of acceleration 
adopted in 1604 rests upon a paralogism. 1 Powerful and original 
as Galileo's thinking already was, and close as it came to the 
essential idea of motion, his kinematics of Euclidean space was 
still a no more complete theory than impetus dynamics. The false 
law of acceleration stated by impetus mechanicians still seemed 
plausible, and Galileo was still ignorant of the true law, explicitly 
stated by Dominico Soto. Galileo had not yet appreciated the 
crucial importance of the distinction between the two possible 

1 This was given in the Discourses (Crew and Salvio, op. cit., pp. 167-9), 
where Galileo used Oresme's calculus of varying qualities to prove that a body 
falls any distance s in the same time if this law of acceleration is adopted. But 
this calculus assumed that the variation in velocity was relative to time, and 
is therefore quite inappropriate. 


hypotheses; an ancient train of thought (strengthened by his 
geometrical proclivities) bound him to spatial relations. Was his 
statement of the distance fallen as a function of time thus a happy 
accident which owes nothing, logically, to the progress of his 
ideas after 1592, since the axiom of 1604 was available to him 
then? Only in a qualified sense. It is true that the geometric 
method of Galileo in 1604 was an attempt to integrate instan- 
taneous velocities in Oresme's graphic representation, but 
Galileo's calculation is purely kinematical. It is not bound in 
terms of explanation to the impetus theory. The quantitative 
result could have been obtained in 1592, but it would have 
belonged to a different pattern. Secondly, the error which 
enabled Galileo to derive a correct function from a false axiom 
was not an accidental error. It was probably inevitable that it 
would be made by anyone at that stage of thought attempting 
the same calculation. 

Actually, the identical error was made in precisely the same 
fashion independently by Descartes and the Dutch physicist 
Isaac Beeckman. 1 Their acquaintance began in 1618, when 
Beeckman was already convinced of the perfect conservation of 
motion: 'quod semel movetur semper eo modo movetur dum ab 
extrinseco impediatur. 5 He also believed (following Gilbert) that 
gravitation was the result of the earth's attractive force. Accord- 
ing to Descartes, Beeckman proposed the following problem: 
'A stone falls from A to B in one hour; it is perpetually attracted 
by the earth with the same force, without losing any of the 
velocity impressed upon it by the previous attraction. He is 
of the opinion that in a vacuum that which moves will move 
always; and asks what space will be traversed in any given time.' 
Offering certain dynamical axioms, therefore, Beeckman asked 
Descartes to furnish him with a mathematical function relating 
time and distance. And Descartes replied with a geometrical 
construction from which he asserted that if the spaces fallen are as 

j, 25-, 4^ 3 8s, etc., the times of fall are as /, , f * J , f J /, etc. 2 
When his demonstration of this function is examined it is 

1 The story of their collaboration is told by Duhem in Etudes sur Leonard de 
Vinci, vol. Ill, by G. Milhaud in Descartes Savant (Paris, 1920) and by A. 
Koyre", op. cit., pp. 99-128. 

2 By Galileo's theorem they are of course /, A/2/, 2/, 2 Vzt, etc. 


apparent that Descartes has done exactly as Galileo did taken 
the instantaneous velocity as proportional to the distance fallen, 
and arrived at a law of acceleration by a process of integration of 
these instantaneous velocities which is as mistaken as Galileo's in 
1604. Beeckman's interpretation of Descartes' geometry is even 
more curious. For Beeckman wrote out a perfect demonstration 
that, from his hypotheses of motion, the instantaneous velocity is 
proportional to the time, and the distance fallen to the square of 
the time, without ever perceiving that it was different from that 
given to him by Descartes, in fact he noted this proof as devised 
by Descartes. Evidently neither Beeckman nor Descartes was able 
to make a clear distinction between the two laws of acceleration: 
neither was capable of seeing that the true function relating 
distance and time can only be deduced from the one hypothesis. 
Thus the investigations of Beeckman, Descartes and Galileo show 
the same intellectual difficulty: even when the essence of motion 
was justly apprehended in physical terms, its geometrical expres- 
sion defeated their initial efforts. The disentanglement of the 
velocity-time and the velocity-distance relationship was still 
hazardous and the sheer mathematical task of integrating 
changing quantities could not be attempted with any assurance 
of success. 

There is evidence to suggest that Galileo had developed the 
correct formulation of acceleration by 1609, but the steps he 
followed are unknown. It may have been that first he discovered 
the error of his calculation, and so was led to substitute the true 
axiom for the false: but it would seem more likely that it was in 
meditating further upon the foundation of the law of acceleration 
in his essential idea of motion that he realized the 'intimate 
relationship between time and motion.' 1 It is doubtful if the 
purely mathematical error would have been apparent to him with 
any clarity (since he repeated the same kind of error in his own 
confutation of his first axiom), whereas he may have reflected 
that velocity and rate of change of velocity may be conceived as 
changes in time irrespective of spatial considerations. Yet if 
Galileo had worked backwards from the relation s ^at 2 , as he 
represented it geometrically (Fig. 6), he may have seen that the 
areas ABC, ADE, can only represent distances (Jztf) because of 
their relative dimensions, and that therefore the dimensions AB, 
1 Crew and Salvio, op. '/., p. 161. 


AD must be in time 

( being 

such moreover that 


\ 2 _ADE\ 
) ""ABC/' 

It may be, indeed, that if the function s = %at 2 is assumed to be 
true, it is easier to deduce the true conception 
of acceleration, than it is to perform the 
inverse and more logical operation (in which 
Descartes and Beeckman failed). At all 
events, Galileo inserted into the Discourses a 
long passage to the intent that the "natural" 
idea of velocity is a rate of change in time, 
and acceleration therefore a rate of change of 
velocity in time, which was written, perhaps, 
in 1609, and followed this by the exposure of 
the reductio ad absurdum in the alternative pro- 
position. What he did not do was to derive the 
definition of uniform acceleration from the 
action of a constant force: though again it 
may be conjectured that Galileo's, and 
Beeckman's, progress towards this definition 
may have been influenced by Gilbert's 
suggestion of gravitation as attraction a 
suggestion which from the causal point of 
view liberates natural acceleration from spatial considerations. 

The law of acceleration and the theorem s \afi derived from 
it are the foundations of dynamics, and dynamics exercised a 
preponderant influence in the evolution of scientific method 
during the seventeenth century. It is no exaggeration to describe 
this double discovery, with all the new structure of thought of 
which it was the crowning achievement, as the justification of the 
new philosophy, as the beginnings of exact science which con- 
sciously set itself to proceed by other ways than those of the past, 
and which hardly doubted that all the past philosophy of nature 
was vain. Yet the law of acceleration had been discussed since the 
fourteenth century, and was defined, admittedly not impeccably, 
by da Vinci and Soto among the more immediate predecessors of 
Galileo. Was the extent of his achievement, then, no more than to 
effect the proper integration which would give the law of distances? 
If this had been all, it would have been a great feat, for the 
perplexities of Descartes and Beeckman show that the law of 
acceleration did not prove a ready key even to the most acute and 

D Velocity * E 

FIG. 6. Time, velocity 
and distance. 


resourceful of his contemporaries. But this was not all; Galileo, 
a less ingenious mathematician, excelled Descartes in a mathe- 
matical problem because he understood the conceptual structure 
into which the key would fit. In fact the single law of acceleration, 
set in the framework of impetus theory, had hardly proved more 
useful in the sixteenth century than the crude observation that 
falling bodies travel more quickly as they approach the earth. Its 
full significance was revealed only when Galileo applied it in a 
context of dynamical theory in which the law of inertia had 
replaced the idea of impetus, a theory so highly abstracted that 
causation, friction, resistance, were no longer considered as 
relevant. To Galileo the law was no longer a descriptive deduction 
from physical principles (as it was to Soto), or an arbitrary 
assumption (as it was to Descartes) but a primary fact, inevitable 
in theory and confirmed by experiment. There are many similar 
instances in the history of science of the isolated statement of an 
anterior phase becoming the core of a comprehensive generaliza- 
tion; so comprehensive, in this case, that Galileo obtained from it 
knowledge of a whole class of mechanical theories. It is the com- 
bined effect of this rapid evolution in thought, requiring clarity 
of definition and elaboration of mathematical expression, the 
re-thinking of the nature of motion and the statement of functions 
making quantitative calculations possible, that determines the 
magnitude of Galileo's achievement. The commentary upon 
Aristotle's physics had been replaced by the mathematical 
scaffolding of a new branch of science. 

Galileo and Descartes 

The strategic lines of the Discourses on Two New Sciences were 
probably sketched out about 1609. The origins of the earlier 
dialogues, in which Galileo discussed cohesion and disputed 
the doctrine that " nature abhors a vacuum," attacked the 
Aristotelean view of the accidentals of motion (that there are 
absolutely light bodies, that velocity is proportional to weight, 
etc.) and began the study of the strength of materials (the other 
"new science") may be traced to a period more than ten years 
earlier, when Galileo, in his most Archimedean manner, was 
introducing into wider fields the principles of the sciences of 
statics and hydrostatics founded by his favourite Greek author. 
Certainly the secret of the trajectory of a projectile was known 


to Galileo by 1609, of which he wrote later, 'truly my first purpose, 
which moved me to speculate on motion, was the discovery of 
such a line (which most certainly when found is of little difficulty 
in demonstration) ; nevertheless I, who have proved it, know what 
pains I had in discovering that conclusion.' 1 The theory of pro- 
jectiles, the propositions relating to the oscillations of a pendulum 
by which Galileo established its isochronous property, and the 
various theorems depending on the principle of the conservation 
of vis viva (momentum) are all straightforward deductions from 
the complementary laws of acceleration and inertia. Fragments 
of this reasoning had been used by Galileo in earlier years; for 
example, the experiment of rolling a ball down an inclined plane 
assumes the conservation of motion or vis viva. Now the whole was 
welded into a single coherent mathematical structure. It was not 
a faultless structure, for a number of Galileo's minor theorems were 
later found to be false, but its foundations were sound. 

With one important exception, the theory of impact and the 
partition of kinetic energy between colliding bodies, the whole of 
seventeenth-century kinematics springs from Galileo's Discourses. 
When, finally, this became the instrument by which Gilbert's 
conception of attractive forces could be interpreted mathe- 
matically, the classical theory of dynamics was created. But if the 
lines of descent are direct, the historical process was complex. 
Galileo's intellectual evolution was by no means unique, though 
it has chronological priority. An independent " modern" tradition 
in dynamics can be traced to the fertile conjunction of Descartes 
and Isaac Beeckman. Other writers also, less strikingly, demon- 
strate a general tendency for the idea of the conservation of 
impetus to be transformed into the conservation of motion. As has 
so often happened in science, the decisive advance was made by 
one man in accordance with a broad progressive movement. 
Moreover, the reaction to the publication of Galileo's dis- 
coveries in 1632 was not simply favourable or adverse. 2 In the 
later seventeenth century the mathematico-mechanical group of 
scientists, the true heirs of Galileo, confided entirely in the essen- 
tial conception of motion developed in the Discourses; in England, 

1 That is, the trajectory according to the usual assumptions of Galilean 
kinematics, in a vacuous, perfectly Euclidean space. Cf. Opere, Ediz. Naz., 
vol. X, p. 229, vol. XIV, p. 386. 

2 The elements of kinematics were indicated in the Dialogues, though a full 
discussion waited for the Discourses of 1638. See below, p. no. 


however, where this group was very strong and produced the 
dominating figure of Newton, the Galilean tradition was partly 
modified by the companion influence of Francis Bacon in the 
direction of more forthright empiricism. Thus Newton completed 
the mathematization of the distinction between the ideal laws 
of motion, and the real motions of terrestrial bodies. The repre- 
sentatives of conservative, anti-Copernican science, such as 
Giovanbattista Riccioli, after a vain attempt to dispose of the 
Discourses altogether, ultimately accepted the law of acceleration 
as a rough empirical truth, a mathematical hypothesis approxi- 
mately agreeing with actual experiments, but continued to oppose 
the philosophy of motion from which this law was derived. This 
attitude was not dissimilar to that adopted by Tycho Brahe with 
regard to Copernicus : the innovations could not be philosophically 
true, but they could, by twisting them a little, be taken as 
quantitatively reliable. Far more important for the development 
of science was the position of the Cartesians, who likewise accepted 
Galileo's law of acceleration as a quantitative statement, while 
opposing Galileo's ratiocination in philosophy. 

Descartes himself would never allow any supreme merit to 
Galileo as a scientist, and in his later utterances, after the crisis 
of 1619-20 in Descartes' intellectual development, he felt himself 
far superior because he alone possessed the true method of 
philosophy. In general the reception in France of Galileo's new 
science of motion was not uncritical: along with Descartes, neither 
Mersenne, nor Fermat, nor Roberval would give complete 
credence to a natural philosophy which applied such a violent 
process of abstraction to the complicated world of experience. 
For Descartes this objection was insuperable, and he finally came 
to regard Galileo as a mere phenomenalist who, lacking insight 
into the total mechanism of the universe, had merely been success- 
ful in isolated feats of mathematical description. Of the Dialogues 
on the Two Chief Systems of the World he wrote in 1634 that Galileo 
philosophized well enough on the subject of motion, but that very 
little of his doctrine was wholly true. He admitted that Galileo 
was more correct when he opposed current notions, and had 
indeed expressed some of Descartes' own ideas it is strange to 
find him identifying Galileo's theorem, s = %at 2 , with that which 
he had himself devised in 1618. Four years later Descartes' 
judgement was more harsh. Although he approved Galileo's 


introduction of mathematical reasoning into physical questions 
and his criticism of scholastic errors, he added that Galileo had 
built without foundation because he did not at all proceed by 
order in his investigations, nor consider the first causes of natural 
phenomena. The abstraction of Galilean science which has been 
its merit in the eyes of many subsequent historians was for 
Descartes its cardinal defect. He had now conceived his own model 
of the universe, and he found the Galilean model too remote from 
reality to be worthy of serious consideration. Its prime requisites, 
such as vacuous space and the constancy of gravitational forces, 
were assumptions contradicted by a true insight into nature. 1 

Descartes was no less convinced of the errors of the past than 
Galileo. He was equally a pioneer of the new natural philosophy. 
But whereas Galileo had arrived at a new method of procedure by 
patient inquiry into particular problems so that his essential idea 
of motion was the product of the endeavour to resolve the incon- 
sistencies in the prevailing conception, Descartes' method taught 
him that it was essential to settle the simplest and most general 
ideas first, and then (as in the three treatises appended to the 
Discourse on Method] particular applications could be made to 
specific problems. What, for instance, is the simplest idea of 
matter? Extension, Descartes replied: matter is that which occu- 
pies space. To suppose that space could exist without a material 
content, that dimension could be conceived without any physical 
consideration, was meaningless. God could formally create a 
vacuum, but so interchangeable were the ideas of space and matter 
for Descartes that if a vessel was imagined to be divinely exhausted 
of matter, it meant only that its walls had been brought together 
so that there was no space between. Of course he admitted that 
vessels could be sensibly exhausted of grosser matter, such as 
water or air, when they would remain filled with a purer species 
capable of passing through the pores in the coarse material of the 
vessel. Similarly with motion: the simplest idea was the translation 
of a body from one situation among other bodies to another 
situation among a different set of bodies, and motion and rest 
were simply states of matter. This definition enabled Descartes 
to declare formally that the earth does not move, since despite its 

1 (Euvres de Descartes, publiees par Charles Adam et Paul Tannery, vol. I 
(Paris, 1897), pp. 303-5; vol. II (Paris, 1898), pp. 380-8. Also J. F. Scott, 
The Scientific Work of Descartes (London, 1952), pp. 161-6. 


revolution around the sun in the vortex of the solar system, its 
environment in surrounding matter is unchanged. Movement, 
properly, was displacement; as a body moves, it is forced to 
displace other matter from its path, and a corresponding quantity 
must occupy the volume which the motion of the body would 
otherwise leave vacant. From these considerations Descartes 
deduced more specific laws. In the first Beeckman's conservation 
of motion became the perpetuation of the state of matter unless it 
is acted upon in some way. In Descartes' second law this principle 
of inertia was perfected by the statement that all bodies in motion 
continue to move in a straight line, again unless they are acted 
upon. Thus the necessity for some centripetal lien or force in 
circular motion was explicitly recognized by Descartes a funda- 
mental contribution to mechanics. The third law of motion was 
the fundamental rule for determining the partition of motion 
between impacting bodies. It was only later that the mistake in 
Descartes' formulation of the laws of impact became significant; 
they were, however, essential to the development of his corpuscular 
philosophy of matter. The notion of an intangible, incorporeal 
force, like Gilbert's attraction, was to Descartes barbarous and 
unthinkable. The state of matter could only be altered by the 
direct action of other matter, that is, by contact between bodies. 1 
Hence what appears as the action of an incorporeal force is in 
reality the action of a stream of impalpable particles. 

Action at a distance such as the gravitational pull of masses 
across empty space was to remain for Cartesians the bitter pill 
of Newtonian mechanics. Implicitly its impossibility conditioned 
Descartes' reaction to Galilean mechanics. When he declared 
that Galileo had not inquired what weight is, when he maintained 
that Galileo's description of how bodies fall was vitiated by his 
ignorance of why they fall, he meant that in nature there are 
no constant forces producing constant accelerations. 'That is 
repugnant to the laws of Nature, for all natural forces (puissances) 
act more or less, as the subject is more or less disposed to receive 
their action; and it is certain that a stone is not equally disposed 
to receive a new motion or an increase of velocity when it is 

1 Thus Descartes was led into an insoluble problem the nature of the 
contact between the soul (spirit) and the matter of the human body. (Cf. M. M. 
Pirenne: "Descartes and the Body-Mind Problem in Physiology," Brit, jf.for 
the Philosophy of Science, vol. I, 1950.) 


already moving very quickly, and when it is moving very slowly.' 1 
Descartes' reasoning is quite clear. Terrestrial gravity he believed 
to be the effect of a stream of corpuscles of impalpable matter 
sweeping towards the centre of the earth. As this stream swept 
through bodies of ordinary coarse matter, it pressed them likewise 
towards the centre. Clearly this pressure would diminish with the 
increasing velocity of the falling body, which would tend towards 
a limit, the velocity of the stream itself. 

fin 1618, under the influence of Beeckman, Descartes had treated 
motion as a geometer, and had made the same sort of mistakes as 
Galileo in 1604. I* 1 later years, at the time when Galileo's treatises 
were published, he thought of motion in the context of physical 
or cosmological theory. Unfortunately, as he penetrated from the 
level of description to the deeper level of explanation, Descartes 
denied himself the possibility of mathematizing the law of 
acceleration: the mechanism, as he framed it, contained too many 
unknown variables. 2 The work in which his system of nature is 
expounded, The Principles of Philosophy (1644), is in fact almost 
completely non-mathematical, although Descartes is one of the 
greatest figures in the history of pure mathematics. For all the 
originality of its starting point, this was a synthetic system, 
blending harmoniously elements derived from the animistic 
science of Aristotle with others taken from the mechanistic 
philosophy of Democritus and Epicurus; and, like these early 
deductive philosophers, Descartes was inevitably preoccupied 
with the uncovering of chains of causation, starting from his 
initial postulates concerning the nature of the physical world. 
When by deductive reasoning the end of the chain was reached, 
it was impossible to adopt the reverse process of analysis and 
abstraction which alone makes a mathematical science possible 
Therefore Cartesian mechanics could never consist of more than 
general principles and the false laws of impact. Therefore also 
Descartes could never do more than admit that Galilean kine- 
matics gave a rough approximation to the real dynamics of the 
world of experience. 

In Descartes the dichotomy between the mathematical and the 
physical attitudes to nature is almost complete, since he could no t 

1 Adam and Tannery, op. cit., vol. I, p. 380. 

2 Koyre*, op. cit., pp. 126-7; Paul Tannery: Mtmoires Scientifiques, vol. VI 
(Paris, 1926), pp. 305-19. 



sacrifice causation to computation. The Cartesians of later genera- 
tions were more eclectic and less rigorous. They could not resist 
the intellectual charms of Descartes' discoveries both in pure 
mathematics and in natural philosophy. In attempting to combine 
them they became the illegitimate heirs of Galileo. Having 
realized the futility of seeking directly for the descriptive dynami- 
cal laws of the actual universe, they sought instead for the correc- 
tion which ought to be applied to the ideal laws of Galileo in order 
to apply them to a world where bodies move in resisting mediums 
and there are no pure forces. No tradition is perpetuated un- 
adulterated and the later Cartesians compromised with the pheno- 
menalism which Descartes had condemned. While they firmly 
maintained his method of philosophizing, his theory of the origin 
of the universe, of the corpuscular mechanisms involved in the 
phenomena of light and vision, magnetism and electricity, gravity 
and the planetary revolutions (none of which, from its very 
nature, could be subjected to direct empirical verification), in 
discussing any problem of mechanical science descriptively they 
turned to the mathematical model of Galileo, to which there was 
no alternative. There was a subtle change of perspective: instead 
of proceeding from indubitable first principles to the details of 
nature and the ultimate descriptive mathematical understanding, 
as Descartes had sought to do, later Cartesian scientists followed 
a different path, that of working out the modifications required 
in transposing a problem from a mathematical model to the 
natural scene. 

This is most true of the Dutch physicist, Christiaan Huygens, 
for many years the mainstay of the French Academic des Sciences. 
Certainly Huygens, when still a boy, had worked out a purely 
mathematical proof of Galileo's law of acceleration, and certainly 
in full age he confessed that his thoughts had been too greatly 
influenced by Cartesian fictions. But it is also clear that he could 
never have become an entire phenomenalist : he was too great 
a Cartesian to be a Newtonian. He has been appropriately con- 
sidered in relation to the Cartesian tradition. 1 Much of Huygens' 
work was suggested by Descartes' own original thoughts (for ex- 
ample, his study of centripetal forces and the laws of impact), 
much of his basic theory was Cartesian. Always denying the reality 

1 e.g. by P. Mouy: La Dfoeloppement de la Physique Cartesienne (Paris, 1934), 
chao. II. 


of a physical vacuum, he believed in impalpable matter or aether, 
and his theory of gravity was wholly in agreement with Descartes'. 
He was never converted to "action at a distance." Yet his particu- 
lar investigations are in the highest class of seventeenth-century 
mathematical physics, and as an experimenter also Huygens, with 
his strong affiliation to the Royal Society of London, was not 
negligible. In the actual conduct of his scientific career no one 
was more justly an exponent of the Galilean tradition in science 
than Huygens who, like Galileo, allied astronomy and physics. 
Only on the widest issues did he fall below the example which 
Galileo had set, when as it seems, measuring the mathematical 
model against the physical model of Descartes, he found his 
attachment to the latter unbreakable. The Cartesian mechanical 
theory of causation in nature was inevitably the frame of reference 
for each of his researches, deeply though his spirit as an inquirer 
was akin to that of Galileo. 

The example of Huygens sufficiently demonstrates the com- 
plexity of intellectual inheritance in the second half of the century. 
There was no simple antithesis, uniform at all points, between 
conventional science and the new philosophy of the scientific 
revolution. There was no pure line of descent in mechanics from 
Galileo to Newton, nor among the scientists of the French school 
who broadly accepted the framework of Cartesian natural philo- 
sophy. The conflict between the Newtonian and the Cartesian 
system of the universe which lasted till about 1 740 was indeed 
absolute and irreconcilable, but it should not be supposed from 
this that the Cartesians had borrowed nothing from Galileo, nor 
that the Newtonians had learnt nothing from Descartes. Much of 
the application of mathematics to mechanical problems which 
had been such a fertile and active field of science during the half- 
century between 1638 and 1687 was in fact the work of men who 
did not subscribe without reservation to Galileo's philosophy of 

In addition, the many lesser contributions to mechanics cannot 
be overlooked. Admittedly the main source-books for the later 
seventeenth century were the Discourses of Galileo and the Prin- 
ciples of Philosophy of Descartes, but other works of the nascent age 
of modern science held fruitful suggestion, among them the prac- 
tical machine-books and even such a curious confection as Baptista 
Porta's Natural Magic. Inventive interest in the development of 


new mechanical devices was a prominent feature in the activities 
of the early scientific societies, the Academic Royale des Sciences 
enjoying the privilege of examining them and officially approving 
those which it found sound and beneficial. Again, though the 
progress in statics during the late sixteenth and early seventeenth 
centuries was less pregnant with consequence than that in dy- 
namicsthere was a profound change in degree rather than a 
change in kind this progress too contributed to the methodology 
of science as well as to the formation of the whole body of experi- 
mental learning. Simon Stevin, whose investigations provided 
another part of the foundations of seventeenth-century mechanics, 
was a man of wide competence little short of the first rank^In 
the history of mathematics he has an important place as, among 
other things, one of the leading early exponents of decimal arith- 
metic.} With another Fleming, De Groot, he carried out, about 
1590, an early experiment on the fall of heavy bodies to test 
Aristotle's theory of motion. In statics his work on parallel forces 
utilized the important principle of virtual velocities or displace- 
ment ; he recognized (like Galileo) that the equilibrium of a system 
of pulleys or levers depends upon the constancy of the product 
of the weight and the distance moved in each of the balanced 
members. Stevin extended the same principle to the action of 
non-parallel forces. He showed that unless perpetual motion is 
assumed to be possible (and Stevin was one of the first to consider 
this ancient fallacy in the light of plain mechanical reason) two 
weights resting upon a pair of inversely inclined planes must 
balance when they are proportional to the lengths of the 
planes. His demonstrations contain the principle of the triangle of 
forces, and therefore the first implication of vector-quantities in 
statics, just as Galileo's treatment of the trajectory of a projectile 
contains the first use of vectors in dynamics. In hydrostatics he 
examined the conditions necessary for the stability of a floating 
body, and the distribution of pressure in liquids, involving a prob- 
lem of integration which he solved successfully. He was the first 
discoverer of the so-called "hydrostatic" or "Pascal's paradox," 
that the pressure of a liquid upon a surface varies only with the 
area of the surface and the height of the column of liquid above 
it, irrespective of its cross-section. This, along with his other dis- 
coveries in mechanics, Stevin described in Flemish in 1586. Isaac 
Beeckman noted it there, and drew the attention of Descartes to 


this strange phenomenon. Descartes without acknowledging his 
source discussed its theory at some length. From Stevin too the 
paradox passed to Pascal, who analysed it very completely in 

The essence of mechanistic philosophy in the seventeenth 
century was the axiom that all natural phenomena could be re- 
duced, by a sufficiently prolonged process of abstraction, to one 
single kind of change, the motion of matter. This axiom was the 
foundation of Cartesian science, and with limitations and qualifi- 
cations it was generally shared by scientific men. Descartes' great 
contribution to dynamics, in a sense, is that he made it the primary 
science. In so doing he caused research to enter some false paths, 
but his idea was to be vindicated in the kinetic theory of the 
nineteenth century. Galileo provided the elements of kinematics, 
the basic conceptualization and the mathematical procedures 
again further elaborated by Descartes in coordinate geometry 
which rendered definable the properties of matter in motion. For 
the next century a major concern of science was the extent to 
which nature could be explained broadly in terms of Cartesian 
mechanism interpreted with the aid of Galileo's descriptive 
analysis of motion. 

1 Milhaud, op. cit., p. 34. 


THE period of silence in which comparatively little comment, 
favourable or unfavourable, was made on the new celestial 
system proposed by Copernicus lasted for about a genera- 
tion after the publication of De Revolutionibus. From the later years 
of the sixteenth century to the middle of the seventeenth there was 
a noisy and not invariably elevated dispute between the adherents 
of the new and the old opinions in natural philosophy in which 
astronomy was the touch-stone of faith. The triumph of the 
innovators did not come rapidly, for it is always easy to exaggerate 
the adaptability of the scientific intellect. Books were written 
assuming the truth of the geostatic system, astronomical clocks 
and armillary spheres were constructed to show a motionless 
earth, until at least the end of the seventeenth century. And it is 
well to remember that though the ascendancy of the "new 
philosophy 55 made modern science possible, the material point 
so often at issue was not of long-term importance. It is now recog- 
nized that before using words like "motion" and "rest 55 in rela- 
tion to the solar system the frame of reference must be explicitly 
defined. It was by no means logically essential to the progress of 
astronomy that men should believe the earth to have an annual 
rotation around the sun. No phenomenon known to the seven- 
teenth century required such a motion for its explanation; in 
practical astronomy the relative movement of earth and sun 
could be equally well interpreted by supposing either to be at 
the centre of the other's orbit. Before the celestial mechanics of 
Newton's Principia was developed, there was no positive, demon- 
strative argument that can be called conclusive either way; only 
in the sense that the progress of science demands the liberty to 
theorize, to extrapolate beyond the available positive knowledge, 
is it true that the Copernicans had enlightenment on their 

The first conflict between the innovators in philosophy and 
authoritarian learning, which was full of consequence in framing 

1 02 


not only the attitude adopted by the Roman Catholic Church 
towards the great astronomical question but also (in part) the 
spirit of the scientific movement, at once defensive against sus- 
pected allegations of irreligion and hostile to the older kind of 
literary scholarship, had strictly no connection whatever with 
natural science. This conflict was exhibited in the famous con- 
demnation of Giordano Bruno. Bruno was burnt in 1600 because 
he taught the plurality of worlds; he was moreover technically an 
apostate from a religious order. He believed that beyond the 
universe we observe there are other universes similar to our 
own, equally of divine creation, equally inhabited by immortal 
souls. Speculation of this kind has a natural fascination for some 
minds; it had occurred very early in the history of systematic 
thought, and had received the strong disapproval of Aristotle. It 
had always been regarded as theologically dangerous. Yet Nicole 
Oresme, in his Livre du del et du Monde gave considerable attention 
to it. He envisaged the possibility of a plurality of worlds in time 
or in space so that there might be one world enclosed in another 
or separate worlds scattered in space, for example beyond "our" 
universe, all the work of one creator. Aristotle's argument that 
the earth of another world would be drawn to a natural place at 
the centre of this he confuted by rejoining that the natural place 
for such earth would be at the centre of its own world. The restric- 
tion of the divine creative power to the fabrication of one universe 
he regarded as a denial of omnipotence. Further, he was bold 
enough to declare that it is natural to human understanding to 
believe that there is space beyond "our" finite universe; in this 
God could bring other universes into existence. From this dis- 
cussion Oresme concluded that reason alone could not eliminate 
the possibility of a plurality of worlds, but that in fact there never 
had been more than one, and probably there never would be. 1 
In the seventeenth century a similar speculation produced the 
first scientific fantasies, such as John Wilkins' Discovery of a World 
in the Moon (1638). 

The allied belief in the infinity and eternity of the whole cosmos 
was also ancient.Expounded by Lucretius, who had them from 
Democritus, these doctrines were further developed by an im- 
portant group of Muslim and Hebrew philosophers of the middle 
ages, though little favoured by Christians. Oresme seems to hint 
1 Medieval Studies, vol. Ill, pp. 233, 242, 244. 


at the infinity of space. Nearer to Bruno's own time the impossi- 
bility of conceiving a boundary to space was asserted by Nicholas 
of Gusa in the fifteenth century: and it was from him that Bruno 
received his inspiration. In his own time the idea was specifically 
related to the Copernican hypothesis by the English mathe- 
matician Thomas Digges. Digges believed the fixed stars to be 
infinitely remote from the earth, a notion he was free to adopt 
since it was no longer necessary to suppose them fastened to a 
revolving sphere. All that the Copernican hypothesis required, 
however, was that the ratio of the distance of the fixed stars to 
the earth's distance from the sun should be a large number; had 
this number been far smaller than it actually is, the sixteenth- 
century astronomer would still have failed to detect any evidence 
of the earth's motion in his celestial observations. As for the 
infinity of space outside "our" universe, it was perfectly recon- 
cilable with Ptolemaic astronomy and not at all a Copernican 
innovation. However great the interest of Bruno's ideas in them- 
selves, the idea of the plurality of worlds was not inspired by the 
scientific renaissance, they were not a logical deduction from 
heliocentric astronomy, and they were totally irrelevant to the 
progress of science. Bruno was not a scientist, and his dispute with 
Rome turned on a purely metaphysical problem. 

It is well to attempt to define the contemporary appreciation 
of a situation such as this. That the introduction of religious 
considerations into a question of quasi-scientific speculation is 
quite distinct from a similar intervention in the interpretation of 
observations or experiments was perfectly clear to philosophers 
of the middle ages and the early modern period alike. A very high 
proportion of scientists up to the mid-seventeenth century were 
men of unusually profound religious conviction, and none used 
science as a lever against religion. Thomas Hobbes won no 
countenance from the Royal Society. The furtherance of science 
and religion were commonly regarded as inseparable objectives. 
The English scientists of the seventeenth century, especially, were 
far more complacent than medieval scholastics in their belief that 
reason and research properly conducted could never conflict with 
religious dogma. The attitude of the middle ages had been that 
where reason was incompetent to decide, faith should pronounce: 
and that in many instances faith must even prevail against reason. 
In the period of the scientific revolution natural theology was still 


distrusted, and divine modification of the laws of nature in rare 
events was a commonplace. A general antithesis between science 
and religion was consequently out of the question; a particular 
antithesis over a single point could only be due to some misinter- 
pretation either of nature or of religious truth. Even for the most 
empirical of scientists, like Boyle and Newton, the introduction of 
religious considerations into the pattern of scientific investigation 
was natural and inevitable. They would not have dreamed of 
denying the validity of a universal moral or religious law a 
concept to them more binding than scientific law. To the Protes- 
tant mind of the seventeenth century the judgements upon Bruno, 
and later Galileo, would seem full of human error and expressive 
of the bigotedly narrow outlook of the unreformed Church, but 
they would agree that it was the duty of the responsible officers 
for the time being to enforce the moral law according to their own 
enlightenment. 1 No sympathizer with Bruno or Galileo believed 
in complete freedom of thought and expression; none would have 
asserted that scientific activity and theorizing are completely 
outside the range of universal moral law. For the seventeenth 
century the burning of Bruno could not be wholly wrong in 
principle as it was to the liberals of the nineteenth. Galileo, though 
he never surrendered his inner conviction of scientific rectitude, 
apparently admitted the right of the ecclesiastical authorities to 
pass religious censure upon his arguments. He lived and died in 
the Catholic faith; and when compelled to make his formal 
recantation, it would seem more reasonable to attribute his 
compliance not to lack of courage, but to recognition of the then 
universal belief that moral and religious truths are of a higher 
order than the scientific. Galileo could only lament that in his 
case the moral law had been misapplied. 

Although the pronouncements of the Holy Office were not 
opposed to any positive scientific knowledge of the time, and in 
the case of Bruno only condemned a form of quasi-scientific 
speculation, they had a deep effect upon the scientific move- 
ment. They were widely interpreted as a final declaration against 
the Copernican system, and there is evidence that some (like 
Descartes) who were disposed to favour a heliostatic model were 
impelled to express their ideas in veiled and guarded terms. It 
seemed as though innovations in natural philosophy must lead to 
1 As the reformed Church of Geneva had upon the person of Serveto. 


outbreaks of heretical opinion, as reactionaries had long predicted. 
Even in England, critics of the newly founded Royal Society did 
not fail to assert that its methods were subversive of the Church 
of England. An odium, which had not existed in the early sixteenth 
century, was for a time attached to any originality in astronomical 
thought. But the challenge provoked a powerful reaction in men 
like Galileo and Kepler. It created a situation in which the new 
doctrines had to be effectively vindicated; it was no longer 
possible for the two systems of the world to exist peacefully side 
by side. 

The pre-Newtonian development of heliostatic astronomy may 
be analysed as involving four principal steps. Firstly, the dissolu- 
tion of the prevailing prejudice against allowing any motion to 
the earth, which involved a careful criticism of all existing 
cosmological ideas in order to create a new pattern in which 
such a motion would no longer seem implausible, and a broad 
discrediting of Aristotle's authority. A necessary auxiliary to this 
was the most important second step, in which physical theories 
were revised to show the invalidity of objections against the 
Copernican hypothesis arising out of terrestrial mechanical 
phenomena. Thirdly, the new astronomy was greatly enriched by 
qualitative observation, which suggested that the old teaching 
was very inadequate. Fourthly, exact quantitative observation 
provided new materials for recalculating the planetary orbits, 
thereby leading to the abandonment of the ancient preconception 
in favour of perfect circular motion, and to the enunciation of 
new mathematical laws. Kepler's discoveries might have been 
expressed in the terms of the geostatic system; but as Kepler was 
a staunch Copernican, his whole discussion of the solar system was 
constructed in such a way as to give further force to the heliostatic 
hypothesis. The accomplishment of these four steps extended over 
a period of roughly half a century (c. 1580-1630), while their 
assimilation and particularly the gradual recognition of Kepler's 
laws of planetary motion occupied another generation. During 
the middle period of the seventeenth century the nature of the 
problem was again slightly changed under the influence of 
Descartes' natural philosophy, which tended to enlarge the dis- 
parity between the natural-philosophical and the mathematical- 
astronomical approach which the discoveries of the first third of 
the century seemed rather to diminish. 


The contributions of Galileo to the first three of these steps were 
of major importance: to the fourth, quantitative observation, he 
brought almost nothing. Galileo was not an astronomer as the 
word had previously been understood, he was never interested 
in the traditional procedures of positional astronomy, but as a 
philosopher he applied new astronomical techniques, mostly of 
his own invention, to the examination of cosmological problems. 
Before 1609 his studies were very largely, if not wholly, devoted to 
physics and mechanics. He must, of course, have been thoroughly 
acquainted with elementary astronomy, and it appears that he 
had already read Copernicus and become converted to his doc- 
trine, which he had at first distrusted. In 1609 Galileo learnt of 
the Dutch optical device which made distant objects seem near, 
and with this hint and considering the invention as a problem in 
optics he constructed his own telescope. During succeeding years 
he endeavoured to increase the magnification of this instrument 
and to effect improvements in lens-grinding, besides carrying out 
celestial observations which were recorded in a series of treatises. 1 
Galileo was the first to appreciate the usefulness of the recently 
invented telescope in astronomy, and was therefore rewarded by 
many discoveries, but within a few years a considerable group had 
taken up qualitative investigation in astronomy. The old and the 
new branches of the subject remained practically distinct until 
about 1670, when the application of the telescope to measuring 
instruments became effective; during Galileo's lifetime astronomy 
with the telescope brought into being a completely new branch of 
scientific investigation. Its first results were striking, and provided 
powerful arguments against Aristotle. In January 1610 Galileo 
saw four of the satellites of Jupiter, which he called the Medicean 
stars and regarded as forming a visible model of the whole solar 
system. Later he observed the phases of Venus, from which it 
could be deduced that the planet revolves around the sun, and 
not between the sun's sphere and the moon's as Ptolemy's hypo- 
thesis supposed. He observed the moon itself, and confirmed his 
conjecture that it was a body resembling the earth, with valleys 
and mountains whose heights he estimated from the lengths of 
their shadows. His telescope resolved part of the Milky Way into 
a dense cluster of stars. The discovery of sun-spots was made by 

1 Sidereus Nuncius ( 1 6 1 o) ; Istoria e dimostrazioni intorna alle macchie solari (1613); 
H Saggiatore (1623), an( ^ t ^ le Dialogues of 1632. 


several observers of whom Galileo was one. They are, of course, 
sometimes visible to the naked eye; Kepler had failed to recognize 
one in 1607 when seeking for a transit of Mercury. Fabricius 
probably made the earliest discovery of these maculae) 
and Scheiner certainly wrote the largest book on them, but 
it was Galileo who realized their importance for astronomical 

To anyone who was prepared to think, the discoveries that 
followed upon the invention of the telescope would suggest a 
single train of thought which was certainly anti-classical but 
equally departed very far from the ideas of Copernicus. It would 
seem that celestial phenomena were much more complex than any 
extant astronomical system allowed. It would seem that the stars 
were not finitely or infinitely remote, but distributed through 
space. It would appear also that the heavens, far from being in- 
corruptible and unchanging, were undergoing regular and irregu- 
lar mutations, as Tycho Brahe had suggested as early as 1572. 
The planets, notably Saturn, whose ring-satellite was not yet 
fully understood, altered their aspects, and the sun itself was 
stained by spots that enabled its revolution upon its axis to be 
traced. The image of the moon could be conceived as comparable 
to that of the earth seen at the same distance. All this tended to- 
wards one general conclusion, that the universe was a physical 
structure, not composed of light and a matter totally different 
from the matter of the terrestrial region, but rather of two types of 
physical body. The first, the stars, were incandescent sources of 
light and plainly physical since they were not invariable. The 
second, of which more could be learnt, the planets, were physical 
bodies practically indistinguishable at this stage from the earth 
itself, which could now be placed without hesitation in the class 
of solar satellites on physical grounds as well as by reason of its 
motion. Physical astronomy was thus a creation of the telescope, 
for in the past the sole subject of astronomical science had been the 
analysis of the positions and motions of the heavenly bodies with- 
out consideration of their nature, which had been resigned to the 
speculative discussions of philosophers, while astrology had em- 
braced the supposed influences of these bodies upon the terrestrial 
region. The concept either of physical astronomy or of celestial 
mechanics (which came later) was completely irreconcilable with 
the philosophic background of sixteenth-century practical astro- 


nomy, and it was necessary to reinterpret the Copernican heliostatic 
universe in this new light. 

This reinterpretation was achieved in Galileo's Dialogues on the 
Two Chief Systems of the World (1623) which was, therefore, far more 
than a mere defence of the heliostatic principle. At the same time, 
it will be seen that Galileo's treatise did not advance beyond De 
Revolutionibus in one respect it retained perfect circular motion 
as a "privileged case" and in another respect it was even far 
inferior, for as a guide to positional astronomy the Dialogues are 
worthless. Galileo wholly neglected the complexities of planetary 
motion with which astronomical theoreticians had struggled for 
two thousand years, and on which his contemporary Kepler was 
to spend his life. In astronomy, Copernicus and Kepler set them- 
selves against Ptolemy; Galileo's opponent was Aristotle, the 

Within a few years after 1609 Galileo's teaching at Pisa as 
modified by his discoveries with the telescope had become uncon- 
ventional enough to occasion his first encounter with the Holy 
Office. The Dialogues were conscious propaganda for the new 
philosophy, though the opinions expressed were put in the mouths 
of imaginary characters. Galileo did not scruple to indulge in a 
certain buffoonery with the Aristotelean Simplicius, whose feeble 
defences are mercilessly attacked. The first pages of the Dialogues 
contain a delightful battle of wits in which of course the Copernican 
is made to score heavily. Galileo examines the reasoning by which 
it is argued that the heavens and the terrestrial region are distinct, 
both in their motions and their natures. He concedes that the 
motions of the heavenly bodies are perfectly circular, since only 
by such motion could the pattern of the heavens be preserved 
without change, and that rectilinear motion 'at the most that 
can be said for it, is assigned by nature to its bodies, and their 
parts, at such time as they shall be out of their proper places, 
constituted in a depraved disposition, and for that cause needing 
to be reduced by the shortest way to their natural state.' 1 But he 
denies that terrestrial bodies do, in fact, move along straight lines, 
and so the antithesis is not a true one. As for the Aristotelean 
contention that the elements move directly towards and away 
from the centre of the universe along straight lines, Galileo replies: 

1 "The System of the World in Four Dialogues," translated by Thomas 
Salusbury in his Mathematical Collections (London, 1661), vol. I, p. 20. 


If another should say that the parts of the Earth, go not in their 
motion towards the Centre of the World, but to unite with its Whole, 
and that for that reason they naturally incline towards the centre of 
the Terrestrial Globe [a notion distinctly reminiscent of William 
Gilbert], by which inclination they conspire to form and preserve it, 
what other All, or what other Centre would you find for the World, 
to which the whole Terrene Globe, being thence removed, would 
seek to return, that so the reason of the Whole might be like to that of 
its parts? It may be added, that neither Aristotle nor you can ever 
prove, that the Earth de facto is in the centre of the Universe; but if 
any Centre may be assigned to the Universe, we shall rather find 
the Sun placed in it. 

A number of propositions in mechanics are carefully elucidated, 
and it is made apparent that the opposition of the Copernican to 
the traditional world-picture will depend upon his completely 
different analysis of the properties of moving things. Mechanics 
in fact is the foundation of cosmology: 

. . . none of the conditions whereby Aristotle distinguished! the Coeles- 
tial Bodies from Elementary [i.e. terrestrial], hath other foundation 
than what he deduceth from the diversity of the natural motion of 
those and these; insomuch that it being denied, that the circular 
motion is peculiar to Coelestial Bodies, and affirmed, that it is agree- 
able to all Bodies naturally moveable, it is behooful upon necessary 
consequence to say, either that the attributes of generable or in- 
generable, alterable or unalterable . . . equally and commonly 
agree with all worldly bodies, namely, as well to the Coelestial as to 
the Elementary; or that Aristotle hath badly and erroneously de- 
duced those from the circular motion, which he hath assigned to 
Coelestial Bodies. 1 

That is, if the earth moves, all Aristotle's physical theory of 
cosmology is baseless. Soon after this, Galileo makes the general 
discussion of the " architectonics" of the world break down on the 
argument that hot and cold are not qualities proper to the heavenly 
bodies. That sort of dictum (he remarks) leads to ' a bottomless 
ocean, where there is no getting to shore; for this is a Naviga- 
tion without Compass, Stars, Oars or Rudder. 5 Accordingly the 
debate shifts to the evidence for or against the changelessness of 
the heavens, in which the new observations made with the tele- 
scope are fully discussed, and a detailed comparison is made 

1 Salusbury, op. cit. y p. 25. 


between the optical properties of the earth and the moon. From this 
their physical similarity is deduced. Incidentally Galileo points 
out the futility of the notion that changes in the celestial region 
would be impossible because they would be functionless in the 
context of human life, the purpose of the heavenly bodies being 
sufficiently served by their light-giving and regular motion. Nor 
does he pass over the curious judgement which made sterile im- 
mutability a mark of perfection: rather if the earth had continued 
' an immense Globe of Christal, wherein nothing had ever grown, 
altered or changed, I should have esteemed it a lump of no great 
benefit to the World, full of idlenesse, and in a word, superfluous.' 
By such asides as these, in a strictly scientific argument, the values 
of conventional thought were challenged in turn, its texture made 
to seem weak and strained. 

The second Dialogue opens with caustic mockery of foolish 
deference to Aristotle's authority: 'What is this but to make an 
Oracle of a Log, and to run to that for answers, to fear that, to 
reverence and adore that? ' Those who use such methods are not 
philosophers but Historians or Doctors of Memory: our disputes, 
says Galileo, are about the sensible world, not one of paper. As for 
the motion of the earth, it must be altogether imperceptible to its 
inhabitants, c and as it were not at all, so long as we have regard 
onely to terrestrial things,' but it must be made known by some 
common appearance of motion in the heavens; and such there is. 1 
But in so far as motion is relative, the science of motion cannot 
decide whether earth or heaven really moves. 2 Consequently 
opinion turns on what is "credible and reasonable." It is more 
reasonable that the earth should revolve than the whole heaven; 
that the celestial orbs should not have contradictory movements; 
that the greatest sphere should not rotate in the shortest time; that 
the stars should not be compelled to move at different speeds with 
the variation of the Poles. On all these points Galileo's view of 
what is " reasonable" supposes a different perspective from that 
of anti-Copernican philosophers; but Simplicius is not allowed to 
argue the matter, and merely remarks that 'The business is, to 
make the Earth move without a thousand inconveniences.' The 

1 Salusbury, op. cit. 9 p. 97. 

2 * Motion is so far motion, and as Motion opera teth, by how far it hath 
relation to things which want Motion: but in those things which all equally 
partake thereof it hath nothing to do, and is as if it never were.' 


first group of " inconveniences " to be dealt with includes the usual 
mechanical phenomena, the stone falling vertically, the cannon- 
ball ranging equally far east and west, which it was thought 
would not occur if the earth moved beneath. They naturally lead 
Galileo into a long exposition of his new ideas on mechanics, in 
which a partial version of the law of inertia is enunciated. Much 
of this reasoning against the Aristotelean doctrine of motion had 
already been exactly anticipated by the impetus philosophers of 
the middle ages. There is a long discussion of the so-called devia- 
tion of falling bodies a problem which attracted attention inter- 
mittently throughout the seventeenth century as affording a 
possible proof of the earth's rotation. It had been alleged, for 
example by Tycho Brahe, that if a stone was allowed to fall freely 
from the top of the mast of a moving ship, it would not fall at the 
foot of the mast, but well aft. Galileo shows that this is inconsistent 
with the true principles of mechanics. In spite of Simplicius' cry 
4 How is this? You have not made an hundred, no not one proof 
thereof, and do you so confidently affirm it for true?', Galileo 
places his faith in a priori reasoning to predict the result of an ex- 
periment he has never made, though previously he has taken pains 
to point out (against Aristotle) that experiment is always to be 
preferred to ratiocination. Therefore, since all heavy bodies have 
inertia: 'we onely see the simple motion of descent; since that 
other circular one common to the Earth, the Tower and our selves, 
remains imperceptible, and as if it never were, and there remaineth 
perceptible to us that of the [falling] stone, onely not participated 
in by us, and for this, sense demonstrateth that it is by a right line, 
ever parallel to the said Tower.' 1 

In his attempt to analyse the true path followed by a falling 
body in space the resultant of its double motion about and 
towards the centre of the earth Galileo committed a serious error 
caused by his imperfect definition of inertial motion. Though 
familiar with the common effects of centrifugal force, he over- 
looked the fact that the inertial motion of the falling stone is along 
a tangent to the earth's surface, so that in the absence of gravity 
it would never describe a circle about the earth's centre unless it 
was held to it in some way, but would continue along a straight 
line into space. Galileo thought, on the contrary, that its inertia, 
impetus or virtus impressa could cause a free body to revolve in a 
1 Salusbury, op. cit., p. 143. 


circle, and so he declared that if a stone fell at a uniform velocity 
towards the centre, its compound path would be an Archimedean 
spiral. Since the motion of descent is accelerated, however, he 
devised a demonstration showing that the true path in space is 
probably an arc of circle. Marin Mersenne, who obtained the 
accurate law of inertia from Descartes, described this curve cor- 
rectly in 1644 as a paraboloid. It is possible that Galileo was in- 
duced to make this error, which he never corrected despite its 
incongruity with the parabolic theory of projectiles worked out 
in the Discourses, because of his preconception in favour of perfect 
circular motion. Eager to prove that even the local motions of 
terrestrial bodies are truly circular, as further testimony against the 
Aristotelean antithesis between circular-celestial and rectilinear- 
terrestrial displacements, he also noted that, on his theory, the 
absolute velocity in space of the falling body is uniform, accelera- 
tion relative to the earth's surface being only apparent. This 
being so, the question of finding the cause of acceleration, which 
had made Galileo doubtful of the original impetus theory many 
years before, could be shown to be spurious; the problem is 
solved by denying absolute acceleration in falling bodies alto- 
gether, and visualizing the phenomenon of relative acceleration as 
the product of the uniform movement of observer and object along 
intersecting circular paths. 

With one exception the mechanical objections that could be 
raised against the earth's diurnal revolution are disposed of by 
appeal to the principles of inertia and of the relativity of motion 
which Galileo illustrates with a variety of ingenious examples. 
Other problems in mechanics auxiliary to the main argument are 
touched upon, such as the conception of static moment, the iso- 
chronism of the pendulum, and the law of falling bodies, here 
quoted by Galileo without proof. In replying to the objection that 
the rotation of the earth would hurl down buildings, etc., Galileo 
makes the first investigation into centrifugal forces. Using the 
idea of virtual forces, enunciated in connection with static 
moment, he proves that with equal peripheral velocities the force 
is inversely proportional to the radius. He points out that the 
angular velocity of the earth is very small, and its radius very 
large: therefore the force set up would not be sufficient to over- 
come a body's natural gravity. From Galileo's argument ('thus 
we may conclude that the earth's revolution would be no more 



able to extrude stones, than any little wheel that goeth so slowly, 
as that it maketh but one turn in twenty-four hours') it is clear 
that he did not realize that when angular velocities are equal, the 
centrifugal force is directly proportional to the radius. It was not 
indeed till much later that the rotatory stresses in equatorial regions 
were detected. 

The extensive illustration of the perfect agreement between the 
heliocentric theory and a rational natural philosophy is certainly 
Galileo's most important contribution to the cosmological debate. 
In this there was no conflict of principle between the new philo- 
sophy and the old: they were agreed that the science of motion 
was the foundation of physics, and that physics and astronomy 
must speak the same language. Galilean mechanics was thus the 
necessary complement to Copernican astronomy, and though it 
is true (as Professor Hcisenberg has remarked) 1 that nothing could 
have been more surprising to the scientists of the seventeenth 
century than their discovery that the same mechanical laws were 
appropriate for celestial and terrestrial motions alike, on the 
smallest and largest scale, the coincidence was not fortuitous, for 
it followed from Galileo's conscious endeavour to interpret 
Copernicus' mathematical model in terms of natural philosophy. 
There could be no question as Galileo frequently emphasizes in 
the course of the Dialogues of proving that the Copernican 
hypothesis was necessarily true; but with the readjustment of 
physical ideas effected by him it could be shown to be at least 
as plausible as the Ptolemaic. Aristotle's physical theory of the 
cosmos, terrestrial and celestial, had been an integral whole; for 
Galileo astronomy and physics were so far independent that he 
acknowledged the incompetence of purely physical observations 
to determine the system of the world, but he had no doubt that 
the same laws of motion were universally applicable, to celestial 
and terrestrial bodies alike, even to the point of satisfying himself 
that if the planets had fallen freely towards the sun from the same 
determinate point, they would have acquired, when they had 
attained their actual orbital distances from it, the velocities with 
which they actually revolve about it. A true mechanical theory, 
besides wholly destroying all physical objections to the helio- 
centric system, actually created a preponderance of belief in its 

1 Philosophic Problems of Nuclear Science (London, 1952), p. 35. 


In the Third Dialogue Galileo takes up the arguments for and 
against the annual motion of the earth. Beginning with purely 
astronomical considerations, he makes plain his distrust of the 
quantitative measurements of his own time, from which, however, 
he confirms that the new star of 1572 was truly celestial. The 
irradiation of light, exaggerating the stars' and planets' apparent 
diameters, is next explained, and the observations are proved to 
verify the Copernican arrangement. Galileo then discusses, in an 
eloquent and lucid exposition, the problem posed by the absence 
of a detectable stellar parallax. He was not of the opinion that the 
stars are infinitely remote, but he does argue that the size of the 
universe is such that its dimensions are beyond human standards 
of magnitude. If its immensity can be grasped, then it cannot be 
beyond the power of God to make it so immense; if its immensity 
is beyond comprehension, it is none the less presumptuous to 
suppose that God could not create what the mind cannot compre- 
hend. Simplicius objects that a vast region of empty space between 
the orbit of Saturn and the fixed stars would be superfluous and 
purposeless, so that Galileo can again condemn the introduction 
of teleological reasoning into science. 1 He appears to think that 
the remoteness of the fixed stars, though vast, is not to be exag- 
gerated, and calculates that even if the radius of the stellar sphere 
bore the same proportion to the semi-diameter of the earth's 
orbit, as that bears to the radius of the earth, a star of the sixth 
magnitude would still be no larger than the sun, which is, 
according to Galileo's reckoning, five and a half times as big as 
the earth. The assiduity and skill of astronomers in making 
observations of stellar parallax is in any case doubtful, since these 
would demand 'exactnesse very difficult to obtain, as well by 
reason of the deficiency of Astronomical Instruments, subject to 
many alterations, as also through the fault of those that manage 
them with less diligence than is requisite. . . . Who can in a 
Quadrant, or Sextant, that at most shall have its side 3 or 4 
braccia long, ascertain himself. . . in the direction of the sights, not 
to erre two or three minutes?' 2 

Galileo's general explanation of the manner in which the 
heliocentric theory ' 'saves the phenomena" is modelled on that 
of Copernicus, save that he denies the reality of the third motion 

1 A teleological argument is, however, used by Galileo himself later. 

2 Salusbury, op. cit., vol. I, p. 351. 


which Copernicus had ascribed to the earth in order to account 
for the parallelism of its axis. Thus, for instance, the principle of 
the relativity of motion solves the appearance of stations and 
retrogressions in the planets. But Galileo nowhere indicates that 
their orbits, which Copernicus had made eccentric, are other than 
purely circular about the sun, nor does he attempt to justify 
particular orbits from the records of positional astronomy. He 
further differs from Copernicus in making the centres of the orbits 
coincident with the body of the sun. It cannot be said, therefore, 
that Galileo improved the Copernican argument in terms of 
technical astronomy in the Dialogues, except through his use of 
the new qualitative evidence derived from the telescope, which 
had already been commented upon in his earlier writings. Indeed, 
the extremely simple astronomical model described is flatly 
incompatible with precise observation. Galileo, it is clear, was 
far more confident of the truth of the mechanical principle that 
bodies possess the property of inertial rotation in a perfect circle 
than of the accuracy of astronomical measurements. It was a 
characteristic of his scientific method of abstraction that it could 
more easily analyse, and describe in mathematico-mechanical 
language, a version or model of the real phenomena which was 
less complex than the phenomena themselves; and Galileo was 
not always sufficiently conscious of the genuine significance of the 
greater complexity. In this instance Galileo was deceived, partly 
by his imperfect definition of inertia (only implicitly rectified in 
his discussion of centrifugal force) and partly by lingering astro- 
nomical ideas. It is noteworthy that, while he does not consider 
whether the spheres are real or not, the word itself he uses naturally 
and without comment. A perfectly balanced, hollow sphere, or a 
circle, could of course be properly imagined to rotate inertially as 
a rigid body carrying round with it a planet. It seems, therefore, 
that Galileo, whose approach to the problem was kinematic 
rather than truly dynamic, did not sufficiently reflect upon the 
consequences of taking away the heavenly spheres, and leaving 
the stars and planets as free bodies in space if indeed this was 
firmly his conviction. Unlike Newton, Galileo never compared 
the motion of a planet to that of a projectile; unlike Kepler, he 
did not know that the geometry of planetary orbits vitiated any 
kind of spherical model. 

The scientific work of Johann Kepler (1571-1630) was of an 


utterly different quality from that of Galileo. The Dialogues, and 
to a less extent the Discourses, are popular books. In them Galileo 
does not fear to explain many elementary matters with which the 
expert would already be well acquainted. Kepler's writings, on 
the other hand, are so highly abstruse that the spread of his ideas 
was retarded by the difficulty of discovering and understanding 
them. They required that the reader be fully trained in the 
elaborate mathematics of positional astronomy. As Galileo was 
complementary to Copernicus, so the mathematician Kepler was 
complementary to Galileo, and there is perhaps no more remark- 
able example of the way in which two cognate, yet unlike, minds 
can follow parallel paths without interaction. Both Galileo and 
Kepler sought to strengthen the Copernican doctrine; they 
corresponded, and referred favourably to each other; but there 
is no shred of evidence that either was to the slightest degree 
deflected from his own course, or impelled to modify his own 
ideas, by the other's work. The synthesis of their two distinct points 
of view was only effected a generation later; until then Kepler 
and Galileo had as little in common as Ptolemy and Aristotle. As 
in the traditional, so also in the new science of the early seven- 
teenth century this failure to overlap was not due to fortuitous 
causes, nor to any lack of sympathy between the two modes of 
approach. It was simply that the key by which a synthesis could 
be effected was not yet found. A cosmological dichotomy existed 
in Hellenistic science because physics and positional astronomy 
required similar, but not identical models; a comparable dicho- 
tomy existed from about 1630 to 1687 because there was no way 
in which the observed celestial motions could be interpreted in 
accordance with the kinematical principles of Galileo. The two 
lines of progress could only be brought together by a higher 
generalization for which dynamics was essential and kinematics 

Kepler was the discoverer of the new descriptive laws of plane- 
tary motion, but he achieved more than this, for he made the 
first suggestions towards a physical theory of the universe adapted 
to the necessities of the new description. Although his life was 
given over to mathematical drudgery in which he was aided by 
the much improved trigonometry of his day, and the invention of 
logarithms Kepler was a man of vigorous and original scientific 
imagination. The mathematical operations he set himself could 


hardly have proved creative without it. In his first work he sought 
for the divine canon in celestial architecture, and this pursuit 
ran through all his later computations. But Kepler was no empty 
theorist: the divine art of proportion, the harmony of the grand 
design of nature, was to be elucidated from the most precise 
mathematical observation of the universe. Hence the turning- 
point in his career, the necessary foundation for his work, was 
Kepler's encounter with the Danish astronomer, Tycho Brahe 
(1546-1601), who, after a quarrel with King Christian IV, had 
deserted his royally endowed observatory at Hveen to enter the 
service of the eccentric Emperor Rudolph II, patron of alchemists 
and astrologers, at Prague. Thither Kepler was drawn from Graz 
in Styria by the undigested mass of observations, of unparalleled 
accuracy, which Tycho had brought with him. Ultimately the 
accumulated result of thirty years' labour yielded up the three 
laws of planetary motion which, as Kepler framed them, contained 
the decisive argument against the geostatic hypothesis so warmly 
defended by Tycho. 

In many ways the Danish astronomer's role in the early history 
of modern astronomy is analogous to that of Vcsalius in anatomy. 
Perhaps he was even more fully than the anatomist the iirst 
modern exponent of the art of disinterested observation and 
description. For if Tycho imported into his astronomical theory 
dominant factors which were physical in nature, it cannot be 
said (as it may of Vesalius' physiological preconceptions) that the 
evidence to confute them lay before his eyes. The problem of 
attaining precision was no less real for him than for Vesalius, and 
the methods he devised to solve it were probably more original. 
And certainly Tycho was unique among early modern scientists 
in his insistence upon the crucial importance of accurate quanti- 
tative measurement; always a desideratum in astronomy, cer- 
tainly, but never previously handled with the analytical and 
inventive powers of Tycho, who first consciously studied methods 
of estimating and correcting errors of observation in order to 
determine their limits of accuracy. The most accurate predecessors 
of Tycho were not Europeans, but the astronomers who worked 
in the observatory founded at Samarkand by Ulugh Beigh, about 
1420. Their results were correct to about ten minutes of arc 
(i.e. roughly twice as good as Hipparchus'); Tycho's observations 
were about twice as good again, falling systematically within 


about four minutes of modern values. 1 This result was achieved 
by patient attention to detail. The instruments at Hveen were 
fixed, of different types for the various kinds of angular measure- 
ment, and much larger than those commonly used in the past, 
so that their scales could be more finely divided. They were the 
work of the most skilful German craftsmen, whom Tycho en- 
couraged by his patronage and direction. He devised a new form 
of sight, and a sort of diagonal scale for reading fractions of a 
degree. In measuring either the longitude of a star, or its right 
ascension, it is most convenient to proceed by a way that requires 
an instrument measuring time accurately, and Tycho studied the 
improvement of clocks for this purpose: but he found that a new 
technique of his own by which observations were referred to the 
position of the sun was more trustworthy. He was the first 
astronomer in Europe to use the modern celestial coordinates, 
reckoning star-positions with reference to the celestial equator, 
not (as formerly) to the ecliptic. Another innovation in his 
practice was the observation of planetary positions not at a few 
isolated points in the orbit (especially when in opposition to the 
sun), but at frequent intervals so that the whole orbit could be 

The techniques and standards of precision in astronomy, of 
which Tycho was the real founder, were evolved slowly over a 
period of thirty years to fulfil a very simple ambition. When he 
made his first observations with a home-made quadrant, he found 
that the places given in star-catalogues were false, and that events 
such as eclipses occurred as much as two or three days from the 
predicted times. As the Copernican "Prutenic Tables" were 
computed from old observations they had brought in no significant 
improvement. The task Tycho set himself, therefore, was very 
simple: to plot afresh the positions of the brightest stars, and with 
the fundamental map of the sky established to observe the motions 
of sun, moon and planets so that the elements of their orbits could 
be recalculated without mistake. It does not seem that he under- 
took this with any violently partisan intent, but it is likely that he 
wished to show the falsity of the Coperni cans' claim to have 

1 As was first pointed out by Robert Hooke, the unaided human eye is 
incapable of resolving points whose angular separation is less than about two 
minutes of arc, so that Tycho's work approximately attains the minimum 
theoretical limits of accuracy for instruments such as he used. 


increased the accuracy of celestial mathematics, and to bolster 
up the geostatic doctrine by publishing unimpugnable tables and 
ephemerides calculated upon that assumption. To vindicate the 
"Tychonic" geostatic system was the last ambition of his life, 
which he charged Kepler to fulfil. However, he was no slavish 
adherent to conventional ideas. He did not believe that apparent 
changes in the sky were due to meteors in the earth's atmosphere; 
he proved that comets were celestial bodies, and that the spheres 
could have no real existence as physical bodies since comets pass 
through them; and his description of the planetary motions 
is relativistically identical with that of Copernicus. 1 As an 
astronomer, indeed, Tycho in no way belonged to the past: it 
was as a good Aristotelean natural-philosopher that he believed 
the earth incapable of movement. 

Tycho's observations, including his catalogue of 1,000 star- 
places, have not proved of enduring value. The earliest observa- 
tions that have an other than historical interest are those of the 
English astronomer, Flamsteed, early in the eighteenth century 
(error c. ten seconds of arc), for within about sixty years of Tycho's 
death the optically-unaided measuring instrument, still ardently 
defended by Hevelius of Dantzig, was beginning to pass out of 
use. Within a century Tycho's tables had been thoroughly revised 
by such astronomers as Halley, the Cassinis, Roemer and Flam- 
steed. In the interval, however, Kepler's discoveries based on 
Tycho's work had become recognized. To appreciate the relation- 
ship between Kepler and Tycho the inventive mathematician 
and the patient observer it must be realized that the balance of 
choice between Keplerian and Copernican astronomy is very 
narrow. Until measurements were available whose accuracy 
could be relied upon within a range of four minutes, or even less, 
there was no need to suppose that the planetary orbits were any- 
thing other than circles eccentric to the sun. Kepler, in plotting 
the orbit of Mars, from which he discovered the ellipticity of 
planetary orbits in general, was able to calculate the elements of 
a circular orbit which differed by less than ten minutes from the 
observations. It was only because he knew that Tycho's work was 
accurate within about half this range that he was dissatisfied and 

1 The point about comets was not noticed by Galileo, some of whose other 
arguments cannot be directed against the "Tychonic" version of the geostatic 


impelled to go further. Kepler's famous "First Law" was thus the 
first instance in the history of science of a discovery being made as 
the result of a search for a theory, not merely to cover a given set 
of observations, but to interpret a group of refined measurements 
whose probable accuracy was a significant factor. Discrimination 
between measurement in a somewhat casual sense, and scientific 
measurement, in which the quantitative result is itself criticized 
and its range of error determined, only developed slowly in other 
sciences during the course of the scientific revolution. 

While Kepler's discoveries would have been impossible without 
the refinement of observation attained by Tycho Brahe, more than 
mathematical precision was involved in them. Before the tele- 
scope, the only materials available for the construction of a 
planetary theory were angular measurements principally deter- 
minations of the positions of the planets in the zodiac when sun, 
earth and planet were in the same straight line. Consequently the 
most that a planetary theory could achieve was to predict the 
times at which a planet would return to the same relative situa- 
tion, and its position at those times. The mathematical analysis of 
the solar system as a number of bodies moving in three-dimensional 
space had never been attempted, as such, by the older astronomers, 
who had been content to assign such problems to philosophers. 
They had never concerned themselves with the real path of a 
planet in space, so long as their model predicted with tolerable 
accuracy the few recurrent situations in which observations could 
easily be made. The whole tendency of the scientific revolution was 
to rebel against this view of the astronomer as a mathematician, a 
deviser of models to save the phenomena, and to see astronomy 
as a science comprehending the totality of knowledge concerning 
the heavens and the relations of the earth to the celestial regions. 
Copernicus had abolished the equant because it was a mathe- 
matical fiction, an unphilosophical expedient. Galileo modified 
Copernicus' universe even further in the direction of physical 
explicability. Kepler had a true conception of the universe as a 
system of bodies whose arrangement and motions should reveal 
common principles of design or in more modern language, be 
capable of yielding universal generalizations which were to 
be demonstrated from the observations, not from physical or 
metaphysical axioms. For Kepler the astronomer's task was not 
to study the universe piecemeal to construct models for each 


separate planet but by studying and interpreting it as a whole 
to prove that the phenomena of each part were consistent with 
a single design. His aim was to provide a fitting philosophical 
pattern for the new discoveries of mathematical astronomy: c so 
that I might ascribe the motion of the Sun to the earth itself by 
physical, or rather metaphysical reasoning, as Copernicus did by 
mathematical,' he remarked in the preface to the Cosmographic 
Mystery. Exact science might properly make inroads upon the 
established prerogative of philosophy; it was far from being his 
purpose to expel natural-philosophical considerations from quan- 
titative science altogether. 

Indeed, Kepler's scientific work was critically influenced by his 
attachment to extra-scientific ideas. He had firm preconceptions, 
and he was strongly opposed to mere phenomenalism. Even more 
than Copernicus he was infected with Pythagorean mysticism, 
and fascinated by the primary, foundational significance of purely 
numerical relations. He could elaborately interpret his descriptive 
generalizations in astronomy in the terms of musical harmony 
genuine "music of the spheres"; draw the analogy between sun, 
fixed stars and planets, and God the Father, the Son and the Holy 
Ghost; or discuss the aspects of the planets at the moment when 
the cosmos was created. Some of the questions which he sought to 
answer are, to later minds, absurd or meaningless. Rightly he held 
that the question, why are the appearances thus and not other- 
wise, requires a scientific (rather than a purely philosophic) 
answer, and he was the first astronomer to take a serious grasp of 
it, but for him also such a question as, why are there no more and 
no less than five planets, was also urgent. As Kepler handled it, 
the inquiry involved an unshaken medieval complacency in the 
certitude of knowledge. His first explanation was given in the 
Cosmographic Mystery (1597), where he adopted the theory that 
the design of the universe is modelled upon the series of five 
geometrically regular solid bodies. He had tried in vain to find a 
rationale for the dimensions of the planetary orbits as calculated 
by Copernicus by considering them as mathematical series, or as 
circles described round regular polygons. The number five was 
certainly accounted for in this theory, and moreover Kepler 
found that if the regular solids were supposed to be fitted each 
inside a sphere, and these within each other in a certain order, the 
dimensions of the six spheres so arranged corresponded approxi- 


mately to those of the earth and five planets. In the Cosmographic 
Mystery Kepler argued trenchantly in favour of the Copernican 
system, which he modified in order to make the sun its central 
point, instead of the centre of the earth's orbit. Believing that the 
imperfect agreement between his theory and Copernicus' determi- 
nations might be due to faulty observation, he had good hope of 
confirming it with the aid of the more accurate measurements 
of Tycho Brahe. 

As Tycho's assistant at Prague, Kepler was directed to perfect 
the theory calculated in accordance with the observations on 
Mars by Tycho's Danish assistant, Longomontanus. The result 
was published in the New Astronomy or Celestial Physics, a book sub- 
sidized by the Emperor Rudolph II and published in 1609, eight 
years after Tycho's death had released Kepler from adherence to 
Tycho's geostatic system. His first discovery was that the plane of 
the orbit of Mars passed through the sun (a point in favour of 
Copernicus) and was invariably inclined to the ecliptic. A major 
problem was the planet's unequal velocity in its course. Although 
Kepler restored the equant-point, and so could adjust the varying 
angular velocity of Mars with respect to the sun in different pro- 
portions, he found that no single position of the cquant-point 
would give a rate of variation satisfying all the observations. The 
same difficulty occurred when the earth's orbit was considered. 
Kepler found that its motion was certainly faster when near to the 
sun than when most remote from it, but not in such a way that the 
angular velocity about any arbitrary fixed point within the circle 
was uniform. 1 The problem one after Kepler's own heart was 
to find a theorem denoting this variation in velocity, an equation 
relating the speed of the planet's rotation at any point to its 
distance from the sun. Here Kepler was assisted by a quasi- 
philosophical notion that it was a "moving spirit" in the sun 
itself which caused the planet's circumgyrations. The further the 
planet receded from this spirit, the more weakly its force would 
operate, and so the planet's velocity would lessen. This anima 
motrix is referred to in the Cosmographic Mystery as hurrying along 
the stars (i.e. planets) and comets which it reaches, with a swift- 
ness appropriate to the distance of the place from the sun, and the 

1 This was the first mathematical proof that the motion of the earth (or, 
as Ptolemy would have said, of the sun) is strictly identical with that of the 


strength of its virtue there. 1 The problem Kepler set himself, of 
assigning a determinate motion to a body revolving round a fixed 
point in an eccentric circle so that it moves through equal in- 
finitesimal small arcs in times proportional to its distance from 
the point, is one that can be solved by integration. He used a 
method similar to that by which Archimedes had long before 
evaluated TT, and so arrived at his "second" planetary law, that 
the radius-vector between sun and planet sweeps over equal areas 
of the orbit in equal times. Though his first proof was open to 
criticism, Kepler was later able to satisfy himself that the various 
errors in his method cancelled each other, so that the law was 
rigorously true. 2 

At this stage in his complex and tedious calculations involving 
the geometrical analysis of many theoretical possibilities, as well 
as the continual checking of the predicted motions against ob- 
servations selected from Tycho Brahe's great store Kepler was 
already convinced that the orbit of the earth or a planet could 
not be a perfect circle eccentric to the sun. As he said: 

The reflective and intelligent reader will see, that this opinion among 
astronomers concerning the perfect eccentric circle of the orbit in- 
volves a great deal that is incredible in physical speculation. . . . My 
first error was to take the planet's path as a perfect circle, and this 
mistake robbed me of the more time, as it was taught on the auth- 
ority of all philosophers, and consistent in itself with Metaphysics. 

In calculations of the earth's angular velocity he could assume the 
orbit to be circular, because its ellipticity is small (nam insensile 
est . . . quantum ei ovalis forma detrahit), but in the orbits of the 
other planets the difference would become very sensible. 3 His next 
problem, obviously, was to define the nature of this non-circular 
orbit more closely. He therefore returned to the investigations on 
Mars, in a far more secure position now that he had worked out 
the movement of the observer's platform the earth with greater 
accuracy than before. Experiment showed that the orbit of Mars 
could not, indeed, be circular, for this when compared with the 
observations made the motion of the planet too rapid at aphelion 

1 Kepler: Gesammelte Werke, vol. I, p. 77. 

2 Ibid., vol. Ill, pp. 263-70. 

3 The eccentricity of the earth's orbit is only 0-017, that of Mars is about 
5 times as great, and of Mercury 12 times. The error which constituted 
Kepler's problem increases roughly as the square of the excentricity. 


and perihelion, and too slow at the mean distances. After many 
trials Kepler wrote: 'Thus it is clear, the orbit of the planet is not 
a circle, but passes within the circle at the sides, and increases its 
amplitude again to that of the circle at perigee. The shape of a 
path of this kind is called an oval.' Again, the development of 
Kepler's thoughts was influenced by his idea of the physical 
mechanism which could produce such a departure from the per- 
fectly circular form. He supposed that the oval path was traced 
by the resultant of two distinct motions; the first being that due to 
the action of the sun's virtue, varying with the distance of the 
planet, and the second a uniform rotation of the planet in an 
imaginary epicycle produced by its own virtus matrix. The hypo- 
thetical orbit would be an oval (or rather an ovoid, since its apses 
would be asymmetrical) enclosed within the normal eccentric at 
all points save the apses. Kepler spent much labour in vain at- 
tempts to geometrize this hypothesis so that it could be compared 
with observation. Direct and indirect methods were tried, but 
Kepler finally had to confess that the oval orbit and the theory of 
its physical causation had "gone up in smoke." It was the acci- 
dental observation of a numerical congruity that led him to 
substitute for the oval an ellipse, which he found could be made 
to fit the area-law exactly. Even at this stage he was much dis- 
turbed because he could not give a physical meaning to the 
elliptical orbit, until he satisfied himself that such an ellipse as he 
required would be traced out by a planet supposed to librate on 
the diameter of an epicycle. 

The third of Kepler's great descriptive theorems, that the 
squares of the periodic times of the planets are in the same ratios 
as the cubes of their respective mean distances from the sun, 
which solved the problem upon which he had originally embarked, 
was announced in The Harmonies of the World (1619). This strange 
book, resuming the theme of the Cosmographic Mystery, has the 
same concern with esoteric relationships. Kepler compared the 
instantaneous velocities of the planets at different points in their 
orbits, and expressed these ratios in terms of musical harmony. 
He further compared the velocities of the several planets at their 
nearest approach to the sun; and finally he was induced to com- 
pare, not merely the periods, times and distances of the planets, 
which he had already discovered to be without significance, but 
the powers of these numbers, and so hit upon the "third law." A 


century and a half later, in 1772, a purely empirical formula 
connecting the distances of the planets was used by Johann Elert 
Bode to predict the existence of an unknown planet beyond 
Saturn. His audacity was vindicated by the discovery of Uranus. 
The simplicity and directness which these relations introduced 
into astronomy need no emphasis. The shapes and dimensions of 
the planetary orbits, and the velocities of the planet's motions 
within them, could now be calculated with ease and certitude. 
Kepler's Laws were the observational axioms upon which 
Newtonian celestial mechanics was to rest secure. What is not 
obvious is that Kepler's discoveries were displayed in extremely 
difficult books, published far from the main foci of scientific 
activity in France and Italy, and so were passed over by a genera- 
tion that ignored their true importance. Kepler himself regretted 
the abstruseness of his subject: 

Most hard today is the condition of those who write mathematical 
works, especially astronomical treatises. For unless you make use of 
genuine subtlety in the propositions, instructions, demonstrations and 
conclusions, the book will not be mathematical; if you do use it, 
however, reading it will be made very disagreeable, particularly in 
the Latin language, which lacks articles and the grace of Greek. And 
also today there are extremely few qualified readers, the rest com- 
monly reject [such books]. How many mathematicians are there, 
who would toil through the Conies of Apollonius of Perga? Yet that 
material is of a kind that is far more easily expressed in figures and 
lines, than is Astronomy. 1 

fn truth Kepler was the last of the medieval planetary theorists, 
the last laborious computer and porer over tables. Such methods 
were too tedious for his own generation, excited by discovery and 
the new philosophy, and to a careless reader Kepler's discoveries 
were hidden in the idiosyncrasy of his strange speculation. When 
they were appreciated, new mathematics and new techniques were 
framing a new astronomy. 

But Kepler was more than a mathematician. Perhaps the 
importance of his work, apart from the three famous Laws, has 
not been sufficiently esteemed. The older historians passed politely 
over Kepler's theorizing on physical mechanisms, his love of 
analogy, and all that was ancillary to the main mathematical 

1 "Astronomia Nova," Ges. Werke, vol. Ill, p. 18. 


argument, as so much dross that was best left buried. Now it is 
not difficult to see that Kepler was as original and stimulating 
in his sidetracks as when following the plain mathematical road. 
Certainly his ideas on gravity, on the action of forces at distance, 
are important factors in the prehistory of the theory of universal 
gravitation. The Cartesians ridiculed Kepler's mysterious forces 
seated in the sun, and his appetites of matter, just as they later 
resisted the notion of gravitational attraction. Kepler does make 
odd equivalencies between "soul" or "spirit" and force, never- 
theless his cosmological theory was mechanistically designed and 
designed to give a far more accurate model than those of either 
Galileo or Descartes. It was Kepler who, in the Cosmographic 
Mystery, denounced the traditional belief in material spheres 
which had been left unchallenged by Copernicus, and on which 
Galileo was ambiguously silent: 

Neither indeed is to be feared that the lunar orbs may be forced out 
of position, compressed by the close proportions of [other celestial] 
bodies, if they are not included and buried in that orb itself. For it is 
absurd and monstrous to set these bodies in the sky, endowed with 
certain properties of matter, which do not resist the passage of any 
other solid body. Certainly many will not fear to doubt that there are 
in general any of these Adamantine orbs in the sky, that the stars are 
transported through space and the aetherial air, free from these 
fetters of the orbs, by a certain divine virtue regulating their courses 
by the understanding of geometrical proportions. 

He went on to ask, by what chains and harness is the moving 
earth fastened to its orb? and to point out that nowhere on the 
surface of the globe do men find it embedded in a material 
medium, but always surrounded by air. Kepler, too, must be 
credited, at least as much as Descartes, with the perception that 
there must be some source of force, or tension, within the solar 
system. It could not be a complex of entirely independent bodies 
without mutual interaction. It could not be accidental that the 
planes of all the orbits passed through the sun, nor could the 
variations of the planet's motion the differences in its velocity 
at perihelion and aphelion, for example be explained without 
the supposition that some force was acting upon it. For Galileo 
the universe was simple and dynamically constant: in Kepler's 
far more realistic picture it was highly complex and its dynamical 
condition constantly changing. Thus it was the Keplerian picture 


that enforced the development of celestial mechanics during the 
late seventeenth century. The descriptive and purely empirical 
laws of planetary motion presented a problem that natural 
philosophy could not escape. Kepler had gone far beyond the 
bounds of the astronomical problem of two generations does the 
earth move or not? to assert principles of celestial motion, set in 
a pattern of theorizing upon cosmic physics, which displaced 
traditional doctrines even more thoroughly. 


"\\7"T HILE *ke ear ty sta g es f the scientific revolution in its 
\\ /physical aspects were strongly positive, the first phase 
VV in biology seems by contrast indecisive and inconclusive. 
The sixteenth century witnessed the promulgation of new ideals 
and new methods of study in such fields as botany and zoology, 
or anatomy and physiology, but there was as yet no more than the 
vague promise of the alternative body of knowledge which the 
pursuit of the new ideals and the practice of the new methods 
would construct in due course. Though existing doctrines might 
be criticized, no others had yet taken shape to displace them. 
There were criticisms occasionally of exaggeratedly animistic 
patterns of explanation; but the application of mechanistic 
philosophy to biological problems was not attempted before 
Descartes. As the mind abhors a vacuum, the natural result was 
a lag of theory behind observation. The authority of Galen 
endured longer than that of Aristotle because it was intrinsically 
far more difficult to apply the principles of physics and chemistry 
to the investigation of physiological processes than to apply 
Galilean mechanics to astronomy; astronomers also had the 
advantage over physicians that mechanics was the first science to 
enter a modern stage. The effect of the greater subtlety of the 
questions handled by the biologist was, so to speak, to distinguish 
observation from conceptualization as separate branches of 
scientific activity. Many experiments had been carried out in 
physical science to confirm or disprove directly the Aristotelean 
pronouncements, when as yet the theory of humours or the 
Galenic account of digestion were still untested. Experimentation 
was not deterred by technical difficulties alone, for imagination 
was lacking and the whole framework of ideas which would have 
given meaning to such experiments had still to be created. Those 
that were planned and successfully carried out such as the well- 
known investigation of Sanctorius (1561-1636) into the quanti- 
tative gain in weight of the body by ingestion and loss through 

129 9 


excretion though they produced interesting information, carried 
little or no weight for or against the main strategic ideas of 
medicine and biology. 

In a somewhat similar manner, the advance of the encyclopaedic 
naturalists of the sixteenth century towards a modern scientific 
method was highly specialized and limited in character. The 
naturalist's ideas concerning the origin of organic life, the distri- 
bution of plants and animals, and the reasons for their wide range 
of structure and form, were still for the most part non-scientific in 
origin, or at best derived from very ancient sources. On the other 
hand, he was progressing towards modern ways of classifying and 
describing organisms and of defining the subject-matter of natural 
history. He became less interested in nature-study as an exercise 
in morality; he made a partial distinction between the Flora and 
the Pharmacopeia. This brought the disadvantage, however, that 
as botanists and zoologists became progressively more efficient in 
classification and description, they came near to losing interest in 
all other problems posed by the organic world. The naturalist was 
limited, in the main, to a particular kind of activity ultimately 
inherited from the apothecaries' need to distinguish medicinal 
herbs partly, of course, because it was one task worth doing 
which was within his competence, but partly also because he 
lacked the imagination which would have freed him from the 
influence of tradition. A different kind of biology, or such crucial 
experiments as those of Redi in the seventeenth century on spon- 
taneous generation and those of Mendel in the nineteenth on 
inheritance, was not technically impossible; it did not necessarily 
depend altogether upon laboratories, instruments and the dis- 
coveries of other sciences. It did require which is a great deal 
intellectual originality. It did require the ability to frame questions 
about the living state and ways of proceeding to answer such 
questions. This was very different from the compilation of greater 
and greater masses of the same type of information. 

The vast range of biological and medical science which widened 
out during the nineteenth century was, therefore, represented in 
the sixteenth only by medicine and natural history: and even 
these studies consisted of little more than the endeavour to cure 
disease and herbalism, these being in turn closely linked. The 
various branches of medicine, such as physiology (the function 
of organs in contrast to the arrangement of organs, anatomy), 


pathology, or hygiene were hardly distinguished save as subjects of 
separate treatises by Galen. All parts of medical science, excluding 
surgery, fell under the general surveillance of the physician. Or 
he might become herbalist or zoologist the former in pursuit of 
the medical virtues of plants, and the latter as a comparative 
anatomist. Therefore it is not surprising that physicians had a 
major creative role in the biology of the sixteenth and seventeenth 
centuries, nor that the course of the science was to some extent 
directed by medical interests. Among the botanists many were 
medical men to name only Fuchs, Cordus, Cesalpino, Bauhin, 
Tournefort, and Linnaeus himself. Brunfels, whom Linnaeus 
called the father of botany, and John Ray, Linnaeus' greatest 
predecessor, were exceptions. All the work in human and com- 
parative anatomy, and much microscopy (the famous exception 
being Leeuwenhoek) , was carried out by physicians. Surgeons, 
being on a lower academic, social and intellectual level, to which 
they were firmly suppressed by the energetic corporate interest 
of the physicians, had far less opportunity to add to knowledge. 
The organization of the scientific movement and the system of 
the universities protracted the dual relationship of medicine and 
biology long after it had ceased to be real when books were 
already being written purely on botany, or zoology, or physiology. 
Nowhere was it possible to obtain formal instruction in any of 
these subjects, save as part of a general course in medicine, until 
the middle of the eighteenth century. Teachers of botany (or of 
chemistry) were appointed only to fulfil the needs of the medical 

To the young physician of the later sixteenth or seventeenth 
centuries, ardent for research, many courses were open. He might 
venture on original methods in practice, collect case-histories, 
perhaps contribute to the growing literature of abnormal observa- 
tions and remarkable cures. Or he might, in the humanistic vein, 
seek to improve the general understanding of the magisterial 
texts. Or he might practise anatomy, in which case he would 
certainly dissect many animals. Or he might embark upon de- 
scriptive natural history. But the texture of the scientific work 
involved in all these courses was far from identical. The humanist- 
physician was easily assimilated to the type of the scholar, the 
naturalist-physician to the type of the lexicographer admittedly 
with the development of specialized powers of observation. Neither 


of these courses, at this time, led naturally to the act of experi- 
menting. The problem, however, which comes nearest to the 
physician's work, the understanding of the functioning of the 
human (and, by analogy, the animal) body in health and disease, 
is one that lends itself to observation and experiment. The physi- 
cian must observe and classify diseases, he must also experiment 
in his therapy. Admittedly the physician found his normal ratio- 
cinative background in Galen's ideas, admittedly he proceeded in 
accordance with the accepted theory of the nature of disease and 
of the measures requisite to effect a remedy; even the ascription 
of symptoms to the humoral condition, the amount and timing of 
blood-letting and the preparation of drugs were laid down by 
rules for his guidance more dogmatically than they are today. 
Yet, whatever the teaching, in any age a physician must be some- 
thing of an empiric. He must learn to use his own judgement. He 
must adapt general principles to particular cases. And in the 
sixteenth century the art of medicine was far from static. Apart 
from the great variety of herbal medicaments among which the 
physician had to make his choice, there were the new inorganic 
remedies, such as mercury, and new drugs from the East and West 
Indies. There was a great controversy over the correct procedure 
in venesection. There were new problems syphilis, gunshot 
wounds, scurvy ravaging crews on long ocean voyages, and plagues 
flourishing with the growth of cities. A physician's practice could 
be guided by principles the use of contraries to restore the balance 
of the humours, or analogy (dead man's skull, powdered, in cases 
of epilepsy) but he could be no mere follower of the book, if 
only because the book was an inconsistent and insufficiently 
specific guide. The most important part of medicine was learnt 
through experience, and profitable experience depends on 

Perhaps this lesson was the most enduring contribution made 
by Paracelsus to true science. Naturally when Paracelsus writes, 
for example, ' From his own head a man cannot learn the theory 
of medicine, but only from that which his eyes see and his fingers 
touch . . . theory and practice should together form one, and 
should remain undivided. . . . Practice should not be based on 
speculative theory,' it has to be remembered that "practice" for 
Paracelsus meant something very different from the rationalist 
practice of the modern physician. He accepted the doctrine of 


signatures; he taught the doctrine of the microcosm and the 
macrocosm that forced the physician to become astrologer; to 
him medicine was the study of the occult forces that play upon 
the human body. Within his conception of the physician's practice 
however, he was empirical. The teachings of Aristotle and Galen 
provoked his unmitigated scorn, and he castigated the academic 
physicians who relied upon the theories derived from them. He 
claimed himself to have learned the art of healing not only from 
learned men, but from wise women, bathkeepers, barbers and 
magicians. Ideally, for him, the test of a remedy was its efficacy, 
though in his devotion to the occult and the esoteric he often fell far 
short of this ideal. Believing that experience was the best teacher, he 
did not hesitate to experiment with medicaments of which the aca- 
demically minded were fearful, and so he became the leader of 
the chemical school in therapy. The strongest poisons, he held (no 
doubt arguing from the virtues of mercury or opium), contained 
hidden arcana, serviceable to the physician initiated into their 
mysteries. No doubt the latitude which Paracelsus introduced into 
medical practice was usually profitless and frequently dangerous; 
but it stimulated a more rationalist empiricism than his own. Not 
for the first time, the experimentalism of magic was favourable to 
the growth of natural science. 

Of course trial-and-error methods do not constitute a new 
philosophy of science. Ambroise Fare's use of ligatures and dress- 
ings instead of cauterization by fire is not to be put forward as an 
example of a conscious experimental science though it was a 
genuine revolt against authority, and a genuine instance of em- 
piricism. Pare knew no Latin: he was only the royal surgeon. But 
it is to a certain degree inevitable that the originally minded men 
who adhered to the more practical aspects of medicine, who were 
compelled to be empirical (Glauber, after all, must have tested 
his sal mirabile), should have moved more naturally in the direction 
of experiment than their colleagues whose interests ran otherwise. 
From dissection for research to experiment of a limited kind is not 
a great step. Anatomical observations on the veins and arteries 
suggested simple experiments on the behaviour of the blood in the 
living body with which venesection made the surgeon necessarily 
familiar. Observations involving vivisection had been made long 
before by Galen and Aristotle, and were repeated in the sixteenth 
century: wounds occasionally gave opportunities for a glimpse 


beneath the surface. There was almost a tradition by which 
poisons and their antidotes were tested upon small animals (and 
sometimes condemned criminals). Moreover, the Hellenistic tradi- 
tion in zoology and physiology offered perhaps the best model of 
experimental science that could be found in the whole corpus 
of transmitted learning. The Aristotle of the Generation of Animals 
and the History of Animals was an experimenter as well as an ex- 
cellent observer. In embryology especially again leaving aside 
all question of theory the sixteenth-century heritage of experi- 
ment is clear. Albert the Great, like Aristotle long before, had 
opened eggs systematically. The men of the renaissance had only 
to continue a well-defined course of investigation. 

Perhaps it is not stretching imagination to see practical medi- 
cine playing somewhat the same role in the development of biology 
as that of technology in the evolution of the physical sciences. The 
physician, engineer and manufacturer had that practical skill in 
their encounters with nature which was lacking to the reflective, 
generalizing philosopher of the study. They wove a strand of 
empiricism into the web of theory. They were equally (if honest 
and intelligent men) more interested in the attainment of tangible 
results than the discussion of means by which such results ought 
to be attainable. And just as experience with cannon or in indus- 
trial chemistry had no simultaneous, directly positive effect upon 
ideas of motion or the four-element theory of matter, so also 
empiricism in medical science could not immediately and pro- 
portionately modify the broad theory of physiology or pathology. 
The impact of empiricism was in all cases gradual, subject to 
variations in emphasis and liable to be different from that which 
posterity might deduce merely by treating practical experience 
as the "cause," and change in theory as the " effect." 

The history of the discovery of the circulation of the blood is 
an illuminating instance of the delayed action of observation and 
experiment upon biological theory. Harvey had little that was 
new in the way of fact available to him. His great merit was to 
integrate known but ineffective facts into a new and comprehen- 
sive generalization. As he himself constantly reiterates in his 
treatise On the Motion of the Heart (1628) for he was one of those 
innovators who had little desire to flout authority unnecessarily 
many of the observations on which he relied were already known 
to Galen. Harvey indeed did not so much contradict Galen as 


gently convert his doctrines. Other observations must have been 
made at almost every venesection if only physicians less intelli- 
gent than Harvey had been able to see their meaning. Though 
their function was imperfectly understood, the valves in the veins 
had been observed more than sixty years before Harvey's dis- 
covery of the circulation was made; the tricuspid and mitral 
valves in the heart, which were also given a rational function for 
the first time by Harvey, had been described by Galen himself. In 
many ways, therefore, Harvey's discovery in biology resembled 
Galileo's in mechanics in being a new interpretation of familiar 
data drawn from common experience, and Harvey, like Galileo, 
had numerous precursors. 

Harvey, however, made a far more precise appeal to experi- 
mental evidence than did Galileo, and his use of a "critical in- 
stance" (though there seems to be nothing to suggest that Harvey 
was at all influenced by his great patient, Francis Bacon) is not 
paralleled in mechanics. The greatest physiologist of the sixteenth 
century, Jean Fernel, had not known how to apply the experi- 
mental method. Sir Charles Sherrington has expressly pointed the 
contrast between him and Harvey: 

Fernel, it would seem, in order to do his work, must find it part of a 
logically conceived world. His data must be presented to him in a 
form which, according to his own a priori reasoning, hangs together. 
In that demand of his lies his inveterate distrust of empiricism. " We 
cannot be said to know a thing of which we do not know the cause." 
And under "cause" he included not only the "how" but the "why." 
With Harvey it was riot so. When asked "why" the blood circulated, 
his reply had been that he could not say. Fernel welcomed "facts," 
but especially as pegs for theory; Harvey, whether they were such 
facts or not, if they were perfectly attested. 1 

To Harvey, anatomy offered the elementary facts of physio- 
logy; Fernel, however, wrote that 'in passing from anatomy to 
physiology that is to the actions of the body we pass from 
what we can see and feel to what is known only by meditation.' 
He had liberated himself from the occult influence of the stars, 
but a mechanistic interpretation of physiological process was still 
alien to his thought. For him the origins of bodily actions had 
to be sought in the soul, the non-material entity controlling and 

1 The Endeavour of Jean Fernel (Cambridge, 1946), p. 143. 


directing the operations of the material parts. In this, of course, 
he simply followed Galen and the Greek tradition. 

The ancients had studied the three most obvious instances of 
the involuntary physiological process respiration, the beating of 
the heart, and the digestion of food and framed a comprehensive 
theory linking and correlating the phenomena. This theory con- 
tained all that Fernel, or any other sixteenth-century physician, 
knew of the matter. In the first place they discriminated between 
three "coctions," the first of which turned the food into chyle, 
transported through the veins of the intestine from the stomach to 
the liver. This movement of the chyle puzzled Fernel, since he 
found the veins full of blood instead of white chyle. In the liver 
the second coction transformed the chyle into blood, which issued 
forth to the various parts of the body. In these parts the third 
coction took place, by which the material absorbed from the 
veins by the flesh was made flesh itself. The coctions were assisted, 
if not effected, by the natural heat of the animal body, being thus 
analogous to ordinary domestic cooking, and each had its specific 
cause in a faculty of the soul. 1 The nutritive faculty, working 
through the natural spirits, was the agent of the first coction; an 
attractive faculty drew the blood from the liver along the veins, 
and from the veins into the flesh. The liver was the source of the 
blood, and the centre from which it flowed out to the parts, in- 
cluding the heart. This flow of blood was not constant, but rather 
an ebb-and-flow alternating motion, by which the humours were 
uniformly distributed about the body. Thus the Ghost in Hamlet 
speaks of the 

. . . cursed hebenon 

That swift as quicksilver it courses through 
The natural gates and alleys of the body. 2 

The Galenic theory certainly did not postulate that the blood lay 
stagnant in the veins, but references to this ebb-and-flow from the 
liver (to which the Latin circulatio was sometimes applied) have 
been misinterpreted as allusions to the true circulation (L. 
circuitio) of the blood. A principal portion of the output of blood 
from the liver passed up the great vein of the body, the vena cava, 

1 Fernel, however, likens the second coction in the liver to fermentation; 
alchemists similarly spoke of the fermentation of metals. 

2 Gates has been interpreted as a reference to the valves, but the alternative 
sense of way, path, is equally possible. 



to the heart, into the right side of which the blood was attracted 
by the heart's active dilatation (diastole) (Fig. 7). At the same 
time air inspired into the lungs was drawn down the venous artery 
(pulmonary vein) into the left side of the heart. During the phase 
of contraction of the heart (systole) blood was squeezed from the 
right side of the heart into the arterial vein (pulmonary artery) for 
the nourishment of the lungs, and also through the median septum 
(the thick wall dividing the heart into two main chambers, or 

Right Atrium 

Right Ventricle 

__ Arterial Vein 
(pulmonary artery) 

Venous Artery 
(pulmonary vein) 

Left Atrium 
Left Ventricle 



FIG. 7. Diagram of the structure of the heart and lungs, illustrating 
the Galenic physiology. 

ventricles) into the left side of the heart. This was the seat of a 
most important operation, for there the blood, already containing 
the "natural spirits" supplied by the liver, was further enriched 
by taking up " vital spirits" from the air. The blood and vital 
spirits were conveyed about the body from the left side of the heart 
by the arterial system. Thus the main function of respiration was 
to introduce vital spirits into the body via the arteries, and of the 
heart to serve as the organ in which this enrichment of the blood 
took place indeed enrichment is an insufficient word, for as 
venous and arterial blood were distinguished by their colour and 
viscosity, as well as by their supposed difference in physiological 


function, it was long denied that they could be the same fluid. 
The venous, alimentary blood was virtually transmuted by the 
addition of vital spirit into the spirituous arterial blood. 

Another joint task of the heart and lungs was to ventilate the 
blood and relieve it of its sooty impurities passing along the 
pulmonary vein and exhaled in the breath. The greater thickness 
of the aorta and other principal arteries was explained on the 
grounds that their dense walls had to retain the fugitive vital spirit, 
but as Harvey emphasized, Galen had not denied that the 
arteries contain blood as well as spirit. The arterial pulse, the 
expansion and contraction of the vessels, was not regarded as 
caused by the similar action of the heart, for Galen judged, as the 
result of one misleading experiment, that the "pulsive force" was 
transmitted along the walls of the arteries. Fcrncl added that if 
the arteries were swelled by the pulse of blood from the heart they 
could not pulsate simultaneously along their length, as they do. 
This belief that the arteries have an active diastole and systole of 
their own in sympathy with those of the heart was still credited 
by Descartes, even though he adopted Harvey's circulation. To 
Fcrnel this active contraction of the arteries also served to squeeze 
the vital spirit into the surrounding flesh. He also, like Johann 
Gunther a little earlier, observed that the phases of the heart and 
arteries are opposite, that when the heart shrinks the arteries 
swell, and vice versa. Some experiments on this seem to have been 
made by Leonardo. The venous system, arising from the liver, 
and the arterial system stemming from the heart were thus 
structurally dissimilar, and since the physiological functions of 
the blood in the veins and the blood and spirit in the arteries 
were also different, they were physiologically distinct also. In 
this theory the active phase of the heart's action was its diastole, 
by which it drew blood, and vital spirit from the air, to itself. 

The Galenical theory was universally adopted by subsequent 
medical authorities, and became familiar to the Latin West from 
the writings of Avicenna and Averroes long before the original 
Greek texts were available or thoroughly understood. Therapeutic 
directions drawn from the theory varied, but the basic facts were 
common to all. The two chief physiological statements of the 
theory: (i) that venous blood nourishes the parts, and (2) that 
arterial blood supplies the parts with vital spirits, were of course 
beyond the experimental inquiry of the sixteenth century. The 


anatomists were, however, able to check upon the agreement 
between the Galenic conception of the blood's motion and the 
observed structure of the venous and arterial systems, and of the 
heart itself. The operation of the valves in the heart offered no 
problem: their opening and closing was perfectly accounted for. 
But the density of the septum imposed an act of faith upon 
Galenical theorists. Berengario da Carpi recorded that the intra- 
ventricular pores in the septum were seen with great difficulty in 
man. Vesalius, probing the pits of the septum, was unable to find 
a passage, and in the first edition of De Fabrica he wrote: 'none of 
these pits penetrate (at least according to sense) from the right 
ventricle to the left; therefore indeed I was compelled to marvel 
at the activity of the Creator of things, in that the blood should 
sweat from the right ventricle to the left through passages escaping 
the sight.' In the second edition he expressed his failure to discover 
Galen's pores even more firmly, and remarked that he doubted 
somewhat the heart's action in this respect. 1 At least one experi- 
ment on the heart is recorded by Vesalius, in which the heart-beat 
of a dog was restored after opening the thorax by artificially 
inflating the lungs. Some anatomists, however, still maintained 
that the passages were easy to find in very young hearts, though 
concealed in the adult body. Meanwhile, the structures in the 
veins, later known as valves, had already been observed by 
Estiennc, and from about 1545 were studied by a number of 
anatomists, such as Amatus Lusitanus (1511-68) who dissected 
twelve bodies of men and animals at Ferrara in 1547 from which 
he derived a wholly false theory of their action. As late as 1603 
these valves were still misunderstood by Harvey's teacher at 
Padua, Fabrizio of Aquapendente. 

Attention was concentrated, not so much on the motion of 
the blood, as upon the physiological function of the heart. If the 
sixteenth-century anatomists had visualized the problem of the 
ebb and flow of the blood in mechanical terms, as a problem in 

1 De Fabrica (1543), Bk. VI, Gh. xi, p. 589; (1555), p. 734: 'However 
conspicuous these pits [in the septum] are, none penetrate (according to sense) 
from the right ventricle to the left through the intraventricular septum; nor 
do those passages by which the septum is rendered pervious present themselves 
to me otherwise than very obscurely, however much they are expatiated upon 
by the teachers of dissection, because they are persuaded that the blood flows 
from the right ventricle to the left. Whence also it is (as I shall also advise 
elsewhere) that I am not a little hesitant concerning the heart's function in 
this respect.' 


hydraulics, the vascular valves would have given them cause to 
think more profoundly; but this was a post-Harveian conception. 
The route of the venous blood to the left side of the heart, 
whence it could issue to the arteries enriched with vital spirits, 
was however open to discovery. Once the impenetrability of the 
septum was granted, such blood could only pass via the pul- 
monary artery, the lungs, and the venous artery. This is the 
so-called "lesser circulation," which is not a circulation at all, 
for those who discovered this path had no notion that any blood 
traversed it more than once. It was not, apparently, an original 
discovery in which Europe has priority. The lesser circulation 
was accurately stated by an Egyptian or Syrian physician, Ibn 
al-Nafis al-Qurashi, in the thirteenth century in the course of a 
commentary on the Canon of Avicenna, in which it was deduced 
specifically from the impermeability of the septum. 1 There is no 
evidence that his statement was known before very recent years, 
so that the sixteenth-century discussions appear to be entirely 
independent. It is significant that in two so different circumstances 
the same observation elicited the same theory. In Europe the 
description of the lesser circulation was first printed by the 
Catalan Miguel Serveto in a theological work, Christianismi 
Restitutio (1553). Serveto was primarily a theologian and though 
he practised medicine it is not certain that he had a medical 
degree. In Paris he was associated with the young Vesalius and 
the veteran Giinther, who spoke of him as an anatomist second to 
none, yet it seems that Serveto's experience in dissection must 
have been brief. He was greatly interested in medical astrology 
and his whole knowledge of medicine seems to be somewhat 
intellectual and literary. There is an element of mystery in the 
sudden introduction of a physiological heresy into a work that 
was almost completely obliterated on account of its religious 
heresy and which was probably written (though not certainly 
with the passage on the circulation) as much as seven years before 
its publication. Serveto had some knowledge of Arabic, and it 
has been conjectured that he may have studied Ibn al-Nafis 5 
text, but it seems unnecessary to postulate that he was less original 
than the thirteenth-century Syrian. Some scholars judge that 
Serveto may have been indebted to the Italian anatomists who 
later described the lesser circulation in print: others think that 
1 On Ibn al-Nafis, cf. Sarton, op. cit. 9 vol. II-2, pp. 1099-1101. 


they were indebted to him. This question of priority is not of 
great importance. 1 

Discussion of the Holy Spirit induced Serveto to write of the 
three spirits of the blood, the soul of the body (Harvey also wrote 
"Anima ipsa esse sanguis"). He denied that there was any com- 
munication through the septum of the heart: instead, 'the subtle 
blood, by a great artifice, passes along a duct through the lungs; 
prepared by the lungs, it is made bright, and transfused from the 
pulmonary artery to the pulmonary vein. Then in that vein it is 
mixed with air during inspiration, and purged of impurity on 
expiration. 5 

The mixture, he said, takes place in the lungs, where the 
spiritual blood is given its bright colour, for the ventricle is not 
large enough for such a copious mixture, nor the elaboration of 
brightness. He imagined channels connecting the artery and vein 
in the lung itself, and argued that the artery was far too large for 
the supply of the lung alone. His physiological conceptions were 
clearly not very different from those of Galen, save that imbibing 
of natural spirit by the blood was extended along the pulmonary 
vein from the heart to the lung. Serveto did not categorically deny 
that blood sweated through the septum: nor, on one interpreta- 
tion, had Galen categorically denied that some blood might pass 
from one side of the heart to the other through the lungs. Such was 
Harvey's understanding of his words: 'From Galen, that great 
man, that father of physicians, it appears that the blood passes 
through the lungs from the pulmonary artery into the minute 
branches of the pulmonary veins, urged to this both by the pulses 
of the heart and by the motions of the lung and thorax.' 2 Though 
it may be doubted that such an interpretation was accepted in 
the sixteenth century, in Serveto original thinking appears to 
emerge tentatively from the ideas of the past. His picture of the 
lesser circulation was very different from that of Harvey. 

The same may be said of intermediate presentations of the same 
idea. In spite of the almost complete destruction of Ckristianismi 
Restitutio^ there is some record of its being read. It has been argued 
that the treatment of the lesser circulation by another Catalan 

1 For the two arguments, cf. H. P. Bayon: "William Harvey, Physician and 
Biologist," in Annals of Science, vols. III-IV (1938-9); and Josep Trueta: 
"Michael Servetus and the discovery of the lesser circulation," Tale Journal of 
Medicine and Biology, vol. XXI (1948). 

2 Robert Willis: Works of William Harvey (London, 1857), p. 44. 


physician, Juan Valverde, in 1554, is imitated directly from that 
of Serveto, since he stated, like Serveto, that the pulmonary vein 
contains both blood and air (later, in 1560, he wrote that it 
contained a copious quantity of blood). Valverde had studied 
under Realdo Colombo from about 1545 at Pisa and Rome; 
remarking that he had frequently observed the anatomical ap- 
pearances with Colombo, he seems to claim no originality for 
himself. Colombo in turn had been a pupil of Vesalius, succeeding 
him for a short space in the teaching of anatomy at Padua, and it 
is possible that the genesis of the idea of the lesser circulation took 
place there, and so was made known to Valverde. Colombo 
certainly claimed the new idea as his own, and hitherto unknown, 
in a treatise published posthumously in 1559, which may well 
have been written before Valverde's printed in 1556. Certainly 
Colombo's reasoning on the circulation is superior to any that 
had preceded it. He made the plain statement that the blood 
passed from the right ventricle through the pulmonary artery to 
the lung; was there attenuated; and then together with air was 
brought through the pulmonary vein to the left ventricle. He relied 
particularly upon the observation that when the pulmonary vein 
is opened it is found to be full of bright arterial blood. 

From this time the circuit through the lungs from the right side 
of the heart to the left was described by a number of anatomists, 
down to the time of William Harvey. It is important to recognize 
that though these physicians are correctly spoken of as precursors 
of Harvey (in the sense that this passage of blood through the 
lungs played a part in the complete theory of the circulation), the 
lesser circulation as it was understood in the sixteenth century 
was not a complete fragment of the whole Harveian theory. 
Harvey understood the lesser circulation in a manner that differed 
significantly from that of his predecessors. For him it was the path 
by which all the blood in the body was transferred from the venous 
to the arterial system: for them it was the path by which a portion 
of the blood formed in the liver and issuing to the parts became 
the blood-and-spirits of the arterial system. For him the pul- 
monary vein contained nothing but arterial blood: for them it 
contained blood and air. The lesser circulation of the sixteenth 
century was, as Serveto said, a great artifice for by-passing the 
impenetrable septum: it led to no other new conception during 
more than sixty years: it did not suggest the general circulation 


because it was really not a circulation at all. Galen's physiology 
was modified, but not entirely displaced. The heart and lungs 
were still not perceived as the operative organs in the vascular 
distribution and the identity of the arterial and venous blood was 
still concealed. The reason for this failure to establish a complete 
idea of the lesser circulation in the sixteenth century is that the 
earlier anatomists were attempting to solve a different problem 
from that of Harvey. They were concerned only to find the route 
by which blood and vital spirits entered the arteries in view of 
the impenetrability of the septum. Harvey's problem was two- 
fold; firstly to account for the function of the valves in the veins 
(which, as was realized before his time, obstructed the flow of 
blood outwards along the veins), and secondly to dispose of the 
large quantity of blood which he knew must enter the heart. The 
novelty of his approach was that it ignored the question of vital 
spirits altogether, concentrating upon a wholly mechanical, and 
partly quantitative, difficulty latent in the accepted doctrine. 
This difficulty had occurred to no one before, because no one had 
doubted that the contents of the veins and arteries respectively 
were absorbed by the parts which attracted them outwards from 
the central reservoirs, the liver and the heart. The early theory of 
the lesser circulation was, therefore, useful to Harvey in that, at 
the proper stage in the development of his own ideas, the transfer 
of blood from the right to the left side of the heart could be fitted 
in as a partially complete portion of the puzzle; but that theory 
in itself was a cul-de-sac so long as it was no more than a variation 
on Galen's. 

Harvey began his medical studies at Padua in 1597, the year of 
his graduation at Cambridge at the age of nineteen. He remained 
there till 1602. His teacher was Fabrizio of Aquapendente, a late 
member of the great Italian school of anatomists and embryolo- 
gists. At this time the lesser circulation was by no means universally 
accepted, and the valves in the veins were still explained in a 
variety of mechanically improbable ways. Robert Boyle, in 1688, 
recorded a conversation with Harvey (d. 1657) in which Harvey 
had said that he was first induced to think of the circulation by 
these valves (of whose existence he must have learnt at Padua) : 

... so placed that they gave free passage to the blood towards the heart, 
but opposed the venal blood the contrary way: he was invited to 
imagine that so provident a cause as nature had not placed so many 


valves without design, and no design seemed more probable than 
that, since the blood could not well, because of the interposing valves, 
be sent by the veins to the limbs, it should be sent through the arter- 
ies and return through the veins. 1 

This doubtless presents a very foreshortened view of the truth, 
but it does relate Harvey very definitely to the Italian tradition 
(as is obvious in many other ways) and it does also indicate 
that Harvey's view of the problem was from the beginning a 
mechanical one. The fact that in De Motu Cordis the valvular 
action becomes one argument among many docs not impugn the 
credit of Boyle's statement. 

It was natural and fitting that Harvey should have traced the 
origin of his discovery to the new anatomy of the sixteenth century, 
for the whole discussion of the vascular system down to his time 
had been based on advances in observation. While the theory of 
the lesser circulation was itself framed in accordance with ana- 
tomical observation, it had not been examined experimentally, 
nor did it contain any new physiological interpretation. On both 
these points Harvey's discovery marks a distinct advance. Firstly, 
he showed that if the vascular system was analysed hydraulically, 
considering the heart as a pump, the veins and arteries as pipes, 
the valves as mechanical valves, the blood itself simply as a fluid, 
conclusive experiments on the flow of blood could be made. For 
this purpose he disregarded " spirits" altogether, though he still 
considered that the heart (not the lungs) restored a spirituous 
quality to the blood. Secondly, he introduced a new physiological 
conception in which the arterial blood was revivifying and restora- 
tive, while the venous blood was the same fluid returning vitiated 
and exhausted to the heart where it received its former virtue 
again. Blood, in fact, was not itself the aliment of the parts, but a 
vehicle carrying the aliment. Harvey's ideas on this were inevi- 
tably vague, and conditioned by the knowledge of his time, but 
he did conceive of the blood regaining in the heart its c fluidity, 
natural heat, and [becoming] powerful, fervid, a kind of treasury 
of life, and impregnated with spirits, it might be said with 
balsam.* As cold precedes death, while warmth belongs to life, 
he saw the heart as the ' cherisher of nature, the original of the 
native fire' whence new blood, imbued with spirits, was sent 

1 Boyle: Works, 1772, vol. V, p. 427. 


through the arteries to distribute warmth about the body. 1 On 
the passage of the blood through the lungs, Harvey's promise to 
explain his conjectures was not fulfilled: but he indicated that he 
thought its function was to temper and damp the blood, to prevent 
it boiling up with its own excessive heat. All Harvey's thought on 
the physiology of the circulation is obviously pre-chemical, proto- 
scientific rather than scientific; it does, however, contain the 
important seminal idea that there is an exchange by which 
"something" is taken up by the venous blood in the heart (really, 
of course, the lungs) and given up by the arterial blood to the 
flesh. Granting the contemporary lack of chemical knowledge, it 
is only open to the criticism that, in eulogizing the heart, Harvey 
strangely overlooked the importance of the fact that venous blood 
becomes arterial in its passage through the lungs from the right 
ventricle to the left, not in the heart itself. Unable to free himself 
completely from the error of his predecessors, he could not quite 
attain the conception of the heart as a pump only, adding neither 
heat nor spirits nor anything else to the blood passing through it. 
Thus Harvey's theory is most perfect in its mechanical aspect, 
which was fully supported by experiment. His purely anatomical 
evidence held little that was new, except perhaps his study of the 
heart as a contractile muscle. He also demonstrated the action of 
the vascular valves, and the correspondence of the cardiac diastole 
with the arterial systole, more forcibly than earlier anatomists. 
Even in anatomy Harvey was successful where his predecessors 
had failed, in deducing that a mass of discordant observations was 
made consistent on the single hypothesis of the circulation of the 
blood; as is most clearly seen in his remarks on the foetal circula- 
tion. The existence of an intercommunication between the pul- 
monary artery and veins, in the mammalian foetus, that disappears 
after birth was familiar to all anatomists, but no one before Harvey 
had correlated this short-circuiting of the lungs with either the 
supposed sweating of blood through the septum, or its passage 
through the lungs. It was left to Harvey to show that the foetal 
circulation avoids the lungs because they are collapsed and 
inactive. He is most original and striking when he uses the 
comparative method: 'Had anatomists only been as conversant 
with the dissection of the lower animals as they are with that of 
the human body, the matters that have hitherto kept them in a 

1 Willis, op. cit., pp. 47, 68. 



perplexity of doubt would, in my opinion, have met them freed 
from every kind of difficulty.' 1 

His admonition was accepted by a host of biologists in the 
later seventeenth century, including Marcello Malpighi who first 
observed the blood passing from the arteries to the veins through 
the capillary vessels in the lungs of a frog the final link that 
clinched Harvey's motion in a circle. Harvey found that the 
action of the heart could be most easily studied through experi- 
ments on small animals or fishes, as for instance observing the 
effect of tying ligatures about the great vessels, in suffusing or 
draining the chambers of the heart. He correlated the single- 
chambered heart correctly with the absence of lungs, and the 
double-chambered heart with the possession of lungs, pointing 
out that the right ventricle, which only sends the blood through 
the lungs, is slightly weaker than the left which sends it round the 
whole body. By experiment Harvey proved that the heart receives 
and expels during each cycle of expansion and contraction a 
significant quantity of blood, not a few drops only: by calculation 
he proved that, on the lowest estimate of the change in volume of 
the ventricles, all the blood in the body passed through the heart 
more than once in half an hour. Even this was a generous under- 
estimate. In his second group of experiments, Harvey further 
demonstrated that the blood moves away from the heart through 
the arteries, and towards the heart through the veins. These 
experiments mainly relate to the human subject, and are such as 
would naturally suggest themselves to a physician practised in 
phlebotomy. Examining the superficial veins of the arm, he 
showed that the limb is swollen with blood when the veins are 
compressed, and emptied of blood when the arterial flow is 
obstructed. He found that the valves in these veins prevented the 
flow of blood away from the heart, and that by arterial manipula- 
tion it was impossible to force blood through them except in the 
contrary direction. Blood always filled an emptied vein from the 
direction of the extremity. Again, he showed that in the jugular 
vein the valves were so constructed as to permit a unidirectional 
flow towards the heart only, and that therefore their function was 
not (as some thought) to prevent the weight of blood falling down 
to the feet. The experience of wounds and venesection was cited 
by Harvey to the same general effect, and he further alleged 

1 Willis, op. cit. 9 p. 35. 


the experience of physicians as proof that the blood was the 
mechanical agent by which poisons or the active principals of 
drugs are rapidly distributed about the whole body. 

It is today far more easy, by taking the truth of Harvey's 
arguments and experiments for granted, to regard his doctrine as 
an obvious and straightforward deduction from the anatomical 
history of two earlier generations, than to appreciate the nature 
of the objections against it. As Galileo remarked in another con- 
nection, once this discovery was made its proof was easy: the 
difficulty was to hit upon it in the first place. Harvey's discovery, 
like Galileo's, was made at a rudimentary level of science, but 
the true measure of the intellectual effort involved is the fact that 
the discovery had escaped all previous anatomists, was greeted 
with incredulity and scorn, and was not universally accepted 
even within twenty years. It seems likely that Harvey himself had 
worked at the problem for at least ten years before he gained the 
solution. Some, as he said, opposed him because they preferred to 
endanger truth rather than ancient belief. Others thought that 
they had discovered technical anatomical arguments against the 
circulation; or that only a portion of the blood circulated; or that 
venous and arterial blood could not be the same fluid. Even the 
basic anatomy of blood-supply to the chief organs of the body 
(especially the liver) was still doubtful, and its physiological 
interpretation barely begun; the capillary circulation, and the 
change in colour of blood, were to remain mysteries long after 
Harvey's death. His originality was that he preferred to face these 
new problems, rather than tolerate longer the inconsistencies of 
the old system, but in this he was followed by few contemporaries. 
As so often in science, one advance was made not by completely 
solving an old problem so that no question remained, but by 
transposing the problem into an answerable form, creating fresh 
problems by the very act of transposition. Harvey asked a question 
which, in his precise terms, had perplexed none of his predecessors, 
and the answer he worked out was important, not only because 
it was correct, or because it challenged prevailing ideas, or even 
perhaps because it introduced a new kind of scientific inquiry. 
Harvey's influence in this last respect was significant (as much in 
his book on generation as in De Motu Cordis) but it was not wholly 
unheralded, and some of the new methods exploited by later 
seventeenth-century physiologists, such as bio-chemical research 


and microscopy, were altogether unknown to him. Perhaps the 
most important of his achievements was to leave unsolved 
problems not blind, impregnable problems, but questions that 
could be answered in the way he had himself declared. Just as 
seventeenth-century mechanics was based upon the unsolved (or 
imperfectly solved) problems left by Galileo, so the experimental 
problems of biology were inherited from Harvey. 

Descartes was not the earliest supporter of the theory of cir- 
culation, but he was the first to try to deduce wider implications 
from it. He himself practised anatomy, and made anatomical 
experiments. He has been accused of plagiarizing from Harvey in 
the Discourse on Method what he himself did not fully understand. 
But he assigned to "an English physician" the credit for the 
discovery of the circulation, and claimed only for himself the 
elucidation of the mechanism of the heart. In his Second Disquisition 
to Riolan (1649), Harvey had himself commented adversely on the 
doctrine of spirits: 'Persons of limited information, when they are 
at a loss to assign a cause for anything, very commonly reply that 
it is done by the spirits; and so they introduce the spirits upon all 
occasions. . . .' 

Harvey's attitude to authority seems to have sharpened with 
age, and in this passage it seems clear that he meant to take 
"spirits" rather as a term in common use, than as having a certain 
existence. At any. rate he declared that the spirits in blood are no 
more distinct from blood than the spirit of wine from wine itself. 
Emphatically, in the Method, Descartes sought to eliminate the old 
idea of spirits from physiology altogether. 1 If the human body 
were purely material, lacking rational or sensitive soul, other than 
natural heat in the heart (which is compared to the heat of fermen- 
tation) it would perform all the functions of the human body 
except that of thought. Descartes illustrated this deduction by the 
motion of the heart, which he imagined to work like a crude 
internal-combustion engine. On contraction, a little blood would 
be drawn into each ventricle, which being suddenly vaporized in 
the hot chamber would cause the whole heart to expand and close 
the inlet valves. This expansion of the blood would also open the 
outlet valves, so that the blood would pass out into the lungs and 
arteries, where it would again condense to liquid and the cycle 
would be repeated. The heat of the heart, about which Harvey 
1 The word was retained, but with a purely chemical meaning. 


had written, thus accounted for its purely mechanical cycle of 
expansion and contraction. In his speculation on the heart, which 
is neither good engineering nor good physiology, Descartes ex- 
ceeded Harvey in the functions he assigned to that organ. It 
supplied heat to the stomach to concoct food; it completed the 
concoction by distilling the blood in the heart 'one or two hun- 
dred times in the day' (according to Descartes, the lungs were 
the condenser in which the blood was restored to the liquid state) ; 
it forced by compression of the blood 'certain of its parts' to pass 
through pores specially designed like sieves to admit them into 
the various parts of the body where they formed humours; and it 
was the hearth where burned a very pure and vivid flame which, 
ascending to the brain, penetrated through the nerves (imagined 
as hollow tubes) to activate the muscles. In On Man Descartes 
developed the theory that the flow of the spirits was controlled in 
the brain by the pineal gland, a sort of valve acting under the 
direction of conscious volition. According to Descartes' study of the 
physiology of behaviour, volition played a minor part even in man, 
who was alone capable of abstract thought and true sensation 
(that is, sensations capable of objective judgement) , and none in the 
activity of any lesser creature. He devoted much attention to the 
study of motor mechanisms and reflex actions as for instance 
tracing the involuntary mechanisms by which, when the hand 
is burnt, the muscles of the arm contract to withdraw it from the 
fire, the facial muscles contract in a grimace of pain, tears flow, 
and a cry is uttered. 1 He regarded the greater part of bodily 
activity as due to mechanical processes of this kind, as automatic 
responses to external stimuli effected by the nervous system; but, 
though Cartesian physiology was to some extent supported by 
anatomical investigation of the relations of nerve, brain and 
muscle, it was in the main a purely conceptual structure. Descartes 
anticipated some of the conclusions of nineteenth-century 
physiology without its careful experimental foundation. 

Harvey's work was an important step towards a mechanistic 
approach to biological problems, containing a tentative challenge 
to the supremacy of spirits founded on a particular experimental 
investigation. Descartes' more comprehensive and more specula- 
tive writings elevated mechanism to a universal truth, in physics 
and biology alike. Soul and material body could have nothing in 

1 Cf. De Homine (Leyden, 1662), pp. 109-10. Sherrington, op. cit., pp. 83-9. 


common save a single mysterious point of contact; nothing could 
be attributed to the soul but thought. The old physiology postu- 
lated a variety of non-material souls or spirits each charged with 
the management of a set of bodily functions; for Descartes those 
functions were the result of mechanistic processes, as much as the 
different appearances and movements of an elaborate mechanical 
clock. This, he said in the Discourse on Method, would not appear 
strange to those acquainted with 

the variety of movements performed by the different automata, or 
moving machines fabricated by human industry, and that with the 
help of but few pieces compared with the great variety of bones, 
muscles, nerves, arteries, veins, and other parts that one finds in the 
body of each animal. Such persons will look upon this body as a 
machine made by the hands of God, which is incomparably better 
arranged, and adequate to movements more admirable than is any 
machine of human invention. 

The body was not maintained alive and active by one or more 
life-forces, or spirits, or souls, but solely by the interrelations of 
its mechanical parts, and death was due to a failure of these parts. 
Therefore, with no non-material factors involved, everything in 
physiology was potentially within the range of human knowledge, 
since no more was required than the investigation of mechanistic 
processes, complex and elaborate indeed. This conception of 
Descartes' was of course premature, far beyond the scope of the 
scientific equipment of his age, and it led to no immediate physio- 
logical discovery. Except perhaps in his work on the eye, the 
factual content of his biological theory was wholly misleading. 
But the influence of his general conception upon the anatomy 
and physiology of the later seventeenth century was profound. 
On the whole, those who tried narrowly to demonstrate its truth 
in particular applications, like Borelli in On the Motion of Animals 
(1680), were least successful, and the attempt to apply mechanical 
principles to medicine failed. Ultimately the intractability of 
nature prompted a return to more vitalistic ideas. On the other 
hand Descartes' justification of experimental inquiry in biology 
was of permanent value. Terms like " vital force" might conceal 
deep ignorance without endangering the investigation of those 
processes through which vital force was supposed to operate. So 
long as spirits or the Paracelsian archeus ruled the body, so long as 
the functions of its organs had been subject to the influence of the 


stars and other occult agencies, it had been futile to interpret 
physiological phenomena in the light of the purely material 
sciences of physics and chemistry. The barrier between organic 
and inorganic must have remained for ever absolute. Experiments 
from which the mystery "life" was excluded would have been 
useless. To have shown that the transformation of venous into 
arterial blood can be effected by oxygenation would have been 
irrelevant to a "spiritual" theory of respiration. The dead liver 
of a corpse could throw little light on the living liver of a man. 
Under Descartes' influence, even at the later stage when his 
mechanism seemed crude to a degree, all this was changed. An 
organ or a limb could be studied as a part of the whole mechanism, 
a cog in the works. It could be assumed that what was found to be 
true of the part in the laboratory must be equally true of the part 
in the living body; that particular results obtainable from certain 
experimental processes when observed in the living specimen 
must be produced by similar processes in its own organization. The 
basic axiom of experimental science is that, circumstances being 
unchanged, a like cause will produce a like result because the 
"cause" releases a chain of events following an unchanging 
pattern. If this is not so, then the experimental method of inquiry 
is not one that can usefully be applied to the problem. It was 
Descartes' discovery (ratiocinative, not empirical) that this was 
true of physiological phenomena; it could be assumed, prima facie, 
that circumstances were unchanged (e.g. between the living 
body and the chemist's vessel), and that since functions were 
automative, like result followed like cause. 

The living state was no longer beyond analysis. Descartes' 
scientific writings, even more than Harvey's, suggested a host of 
inquiries into the nature of physiological process. Those in which 
Descartes had been most interested, pertaining to the operation 
of the nervous system, made little progress before the nine- 
teenth century, though the years immediately after his death saw 
important work in anatomical neurology. The mechanism of 
respiration was tackled more successfully, and a pregnant analogy 
was drawn between combustion and respiration no doubt owing 
something to earlier ideas of the heart as the seat of heat. From the 
members of the Accademia del Cimento through Robert Boyle to 
the eighteenth century a series of investigators studied the effect 
of placing small animals in vacuo y in confined volumes of air, or of 


various " elastic fluids" (gases). It was discovered that in the 
vacuum both combustion and respiration were impossible, and 
that life ceased. It was discovered that a combustible or an animal 
consumed air (the carbon dioxide being dissolved in the water 
which rose up in the vessel), but not all the air, and that the gas 
remaining after combustion ceased would not support life, as 
that which was left after respiration ceased would not support 
combustion. It was further discovered that although vessels could 
be filled with "fluids" that appeared to be air they would not 
support life or combustion. Robert Hooke showed (1667) that a 
dog could be kept alive by blowing into its lungs with a bellows, 
even with the ribs and diaphragm removed, from which he con- 
cluded that the animal 'was ready to die, if either he was left 
unsupplied, or his lungs only kept full with the same air; and 
thence conceived, that the true use of respiration was to discharge 
the fumes of the blood. 3 Other members of the Royal Society 
satisfied themselves by experiment that 'the foetus in the womb 
has its blood ventilated by the help of the dam'; and that the 
foetal circulation depended directly on the maternal. 

For a time, as Hooke's words suggest, there was doubt whether 
the presence of fresh air in the lungs was necessary to remove 
something from the blood (the "sooty impurities" of Galen's 
physiology) or to add something to it. On this point the investiga- 
tions of Richard Lower (1631-91), a physician and an experi- 
mental as well as theoretical physiologist, threw new light. 1 In 
his Treatise on the Heart Lower extended Harvey's discovery and 
defended it against the Cartesian perversions: the heart was not 
caused to beat by a fermentation of the blood, but by the inflow 
of spirits from the nerves, and if the nerves were severed the 
pulsation stopped. The blood, not the heart, was the source of 
heat, and of the activity and life of bodies in this Lower, more 
clearly than either Descartes or Harvey, seems to see the heart as 
nothing but a mechanical pump. Nor has the heart anything to 
do with the change in colour of arterial blood, for this can be 
produced by forcing blood through the insufflated lungs of a dead 
dog, or even by shaking venous blood in air: 

. . . that this red colour is entirely due to the penetration of particles 
of air into the blood is quite clear from the fact that, while the blood 

1 Tractatus de Corde (1669): English translation by K. J. Franklin in Early 
Science in Oxford, vol. IX (Oxford, 1932), especially pp. 164-71. 


becomes red throughout its mass in the lungs (because the air diffuses 
in them through all the particles of blood, and hence becomes more 
thoroughly mixed with the blood) 

venous blood in a vessel only becomes florid on the surface. Lower 
concluded that the active factor in this transformation of the blood 
was a certain "nitrous spirit" (elsewhere called a "nitrous food- 
stuff 55 ) 1 which was taken up by the blood in the lungs, and 
discharged from it 'within the body and the parenchyma of the 
viscera 5 to pass out through the pores, leaving the impoverished 
dark venous blood to return to the heart. Respiration, therefore, 
was a process whose function was to add something to the blood 
(Lower remarked that since "bad air 55 causes disease, there must 
be a communication between the atmosphere and the blood- 
stream); but the fuller understanding of the nature of this addition 
had to await the chemical revolution of the eighteenth century. 

The new ideas of blood as a "mechanical 55 fluid, a vehicle 
for carrying alimentary substances, constituents of the air, and 
warmth around the body, suggested the new therapeutic tech- 
nique of blood transfusion, of which also Lower was a pioneer. 
The blood had still a semi-magical quality, and as it was thought 
that "bad 55 blood could cause debility, frenzy or chronic disease, 
it seemed logical to suppose that if the blood of a human patient 
could be replaced by that of a healthy animal, an improvement 
must result. An Italian who claimed to be the inventor of the 
method of transfusion (though he admitted he had never tried 
the experiment) even suggested that it would effect a rejuvenation 
which should be the prerogative of monarchs alone. Christopher 
Wren (1632-1723), when an Oxford student, made experiments 
on the injections of fluids into the veins of animals, by which, 
according to Sprat, they were 'immediately purg'd, vomited, 
intoxicated, kilPd, or reviv'd according to the quality of the 
Liquor injected.' 2 Suggestions for transfusions of blood between 
animals, and actual attempts to effect it, were made by various 
Fellows of the Royal Society in 1665, and Lower went into the 
matter thoroughly, successfully reviving a dog which had been 
exsanguinated almost to the point of death. Finally, in 1667, 
Lower performed before the Society the experiment of transfusing 
the blood of a sheep into a certain ' poor and debauched man . . . 

1 See below, p. 325. 

2 Thomas Sprat: History of the Royal Society (3rd Edn., London, 1723), p. 317. 


cracked a little in his head,' which the patient luckily survived 
without any change in his condition. In this Lower had been 
anticipated by the French physician Jean Denys, whose practice 
soon after caused the death of a patient, which led to a prohibition 
of transfusion in France and the abandonment of the English 
experiments. Several accounts of this time describe the violent 
reactions produced by the introduction of animal protein into 
the human blood-stream, which rapidly proves fatal, and doubt- 
less much of the apparent success of these early experiments may 
be attributed to the clotting of the blood in the tubes used, 
preventing the passage of more than a small amount. Experiments 
on transfusion were only resumed in the nineteenth century, 
when the use of animal blood was abandoned. 1 

While one important aspect of the expanding experimental 
biology of the seventeenth century was the mechanical and 
biochemical study of the blood, whose functions figured so largely 
in the therapeutical theories of the time, in another the essential 
mystery of "life" was no less involved, and was more directly 
explored. This was the investigation of generation and the em- 
bryonic development of creatures, including man. Just as interest 
in the motion and functions of the blood may be traced to its 
prominent place in the Galenic theory of humours, so these 
embryological researches return in a continuous tradition to the 
work of Aristotle. Of William Harvey himself, certainly one of the 
greatest embryologists of the seventeenth century, it has been said 
that he did not follow the example of some of his predecessors 
in departing from Aristoteleanism, but on the contrary lent his 
authority to a somewhat moribund outlook. 2 On one important 
matter, however, Harvey contradicted Aristotle altogether: he 
was sceptical of spontaneous generation, and if he did not coin 
the phrase omne vivum ex ovo, it epitomizes his thought. The partial 
discredit of spontaneous generation (not complete, for the idea 
was revived in the eighteenth century, when it was refuted 
experimentally by Spallanzani, and again in the nineteenth 
in opposition to Pasteur) was one of the most important changes 
in biological thought of the time; a first step towards modern 
conceptions of the living state. Formerly organisms had been 

1 Cf. Geoffrey Keynes: History of Blood Transfusion, 1628-1914 (Penguin 
Science News 3, 1947). 

2 Joseph Needham: History of Embryology (Cambridge, 1934), p. 128. 


divided into four distinct groups: (i) those that are generated 
spontaneously, (2) vegetative, (3) animal, (4) human. The first 
had only, as it were, a share of the " world-soul"; the others were 
distinguished according to the " souls" of their class. As long as 
these distinctions persisted, founded on fundamental unlikenesses 
attributed to the structure of the world-order reflecting disparities 
in the original created endowment, it was impossible to approach 
the modern conception of life-processes depending upon the 
nature and complexity of the physiological functioning of the 
organism. To make the generalization that the life-process is 
transmitted solely and invariably through specific mechanisms of 
reproduction was a necessary first step towards a rational under- 
standing of the nature of this process, and the differences between 
matter in the living and the non-living state: indeed, there seems 
something fundamentally irrational in the supposition that the 
organization of the living from the non-living might be fortuitous, 
and commonplace at that. The crude, superficial differences 
between the life of a plant and that of an animal are at least 
capable of recognition; but what meaning could be attributed to 
the difference between the life of a spontaneously generated 
mistletoe or worm, and that of other analogous forms? The 
doctrine of spontaneous generation had, moreover, become the 
refuge for superstitions and fables of the most absurd character, 
wholly inconsistent with any serious study of natural history. 

Harvey, it is true, wrote in De Motu Cordis that the heart is not 
found e as a distinct and separate part in all animals; some, such 
as the zoophytes, have no heart,' and he continued, C I may 
instance grubs and earthworms, and those that are engendered of 
putrefaction, and do not preserve their species.' If this was not 
merely a careless phrase Harvey changed his opinion, for in his 
later work On the Generation of Animals (1651), he declared: 

. . . many animals, especially insects, arise and are propagated 
from elements and seeds so small as to be invisible (like atoms flying 
in the air), scattered and dispersed here and there by the winds; and 
yet these animals are supposed to have arisen spontaneously, or 
from decomposition, because their ova are nowhere to be seen. 1 

Before such a statement could be given real force and meaning, 
the arts of natural observation, of comparative anatomy, and of 

1 Willis' Works of Harvey, p. 321. Harvey, however, did not give up the use 
of the term "spontaneous generation." 


simple controlled biological experimentation must be developed 
to, or beyond, the level which they had reached among the 
ancient Greeks. Aristotle's biological knowledge was in many 
respects far superior to anything that was available in the sixteenth 
century indeed some of his observations were not to be verified 
before the nineteenth. It is astonishing to find, for example, that 
Aristotle's sensible and penetrating observation of the process of 
reproduction among bees which itself was not quite correct 
was universally ignored up to modern times, while credence was 
given to fabulous tales of their generation in the flesh of a dead 
calf or lion which, besides appearing in the works of many Roman 
poets and writers on agriculture, were retailed in the sixteenth 
century and later by naturalists like Aldrovandi, Moufet and 
Johnson, and by the philosophers Cardan and Gassendi. Even the 
relatively simple life-cycle of the frog was a mystery, at least to 
academic naturalists. 

Harvey had conjectured that in some cases the invisible "seed" 
of creatures was disseminated by the wind. The man who set 
himself to confute the widespread fallacy of spontaneous genera- 
tion systematically was Francesco Redi (162678), an Italian 
physician who worked under the patronage of the Dukes of 
Florence and was an important member of the Accademia del 
Cimento. 1 His observations and experiments were varied and 
numerous, but the most telling were the most simple. Thus he 
was able to prove, by the simplest means, that decaying flesh only 
generated "worms" when flies were allowed to settle on it; that 
the larvae turned into pupae (which he called eggs) from which 
hatched flies of the same kind; and that the adult flies which 
infested the putrefying material possessed ovaries or ducts con- 
taining hundreds of eggs. Generalizing from such results, Redi 
pronounced that all kinds of plants and animals arise solely from 
the true seeds of other plants and animals of the same kind, and 
thus preserve their species. Putrescent matter served only as a 
nest for the eggs, and to nourish the larvae hatched from them. 
However, he had to admit that there were some examples of 
generation which he could not explain. Intestinal worms and other 
parasites puzzled him, and he failed to discover the cause of the 
growth of oak-galls on trees, which was traced later by Malpighi. 
This led Redi to speculate somewhat loosely on possible perversions 

1 See below, p. 189. 


in the "life-force" of host organisms which might produce para- 
sitic developments. Micro-biology was only coming into existence 
at the time when he wrote, and its absence set a natural limit to 
the range of his investigations. 

Nevertheless, Redi's demonstrations, combined with the later 
work of such naturalists as Malpighi and Swammerdam, were 
generally regarded as sufficiently cogent against the doctrine of 
spontaneous generation. The second half of the seventeenth 
century was a period in which, partly through animal and vege- 
table anatomy, partly through the use of the microscope, and 
partly also through experiment, many of the mysteries concerning 
the less obvious processes of reproduction were being cleared up. 
The sexuality of plants, first asserted by Nehemiah Grew, was 
established experimentally by Camerarius before I6Q4. 1 But if 
the general tendency was for the exclusion of pangenesis, the 
experimentalists were not inclined to hasten towards a purely 
mechanistic interpretation. The embryological speculations of 
Gassendi and Descartes found few followers. Harvey had written, 
* he takes the right and pious view of the matter who derives all 
generation from the same eternal and omnipotent Deity, on whose 
nod the universe itself depends . . . whether it be God, Nature or 
the Soul of the universe, 5 though this did not prevent his studying 
the phenomena with all attention. Similarly, John Ray in the 
Wisdom of God (1693) related his discussion of the fallacy of spon- 
taneous generation to the fixed, created nature of species. Ray's 
world was a machine in the sense that he doubted from the 
cessation of creation on the sixth day the divine institution of 
new species (or the endowment of matter with life de novo) but for 
him life was transmissible only through the recurring generations 
springing from the original ancestors; since the power of living 
was confined to the whole group of creatures extant at any 
moment, it could not be born of any conjunction of purely 
mechanical circumstances. 

Despite the limitations in philosophic outlook, which denied to 
many experienced naturalists and to Harvey in particular any 
vision of the ultimate potentialities of the admittedly crude 

1 When his Letter on the Sex of Plants was published. There were ancient and 
popular forms of this idea artificial fertilization of the date-palm had been 
practised in pre-classical antiquity but it had not acquired any previous 
scientific validity. 


physico-chemical speculations of the time, the history of embryo- 
logy offers a useful example of the critical application of observa- 
tion and experiment to the consideration of scientific concepts 
of a complex order. This was possible for a variety of reasons, 
which point to some significant analogies between the situation 
in this science, and that in the physical sciences where so much 
progress was made. It was important in this branch of biology 
that there were ideas to be challenged or confirmed, problems 
that demanded inquiry, far more obviously than in the purely 
descriptive departments. What were the respective contributions 
of the male and female parents to their offspring? Were the parts 
"formed" or did they merely "grow"? What was the function of 
the amniotic fluid, or the foetal circulation? How was the embryo 
nourished, or enabled to breathe? Aristotle's systematic account 
had attempted to deal with such questions; his exactness in 
biological observation and his acuteness in biological reasoning 
were examined no less thoroughly in the sixteenth and seventeenth 
centuries than were his doctrines relating to the physical sciences. 
As Galileo had wielded the method of Archimedes against 
Aristotle, so in effect Harvey and Redi applied the methods of 
Aristotle as observer against the conclusions of Aristotle as theorist. 
In embryology there was as effective a classical tradition to focus 
attention on the critical points as in cosmology or mechanics. Of 
course the strategic gains were far less there was no dramatic 
scientific revolution but the tactical advance in method and 
analysis was no less real. Though to later minds some of the 
questions asked by the seventeenth-century embryologist are 
meaningless, though the teleological cast of his thought has 
proved fruitless, the tradition of investigation has continued 
unbroken, and some descriptions of observations made at this 
time have never been surpassed. The difficulties to be overcome 
in any analytical department of biology were far greater than 
those which the new mechanics solved, while in addition the 
biologist lacked the logical procedures of physical science. Serious 
limiting-factors in the development of those subjects were to 
disappear only in the nineteenth century: in the late seventeenth, 
however, their techniques were greatly enriched by the use of the 
microscope, which will be discussed in a later chapter. 



CONSCIOUS reflection on the relations between man and his 
natural environment can only be a product of an advanced 
state of civilization in which abstract thought flourishes. 
Greek philosophers seem to have been the first to discuss the 
problem, how can reason be most successfully applied to under- 
standing the complex phenomena of material things? and in so 
doing they introduced the generalizing of ideas that is essential 
to science and distinguishes it from the ad hoc solving of practical 
problems undertaken in man's struggle with nature. It is generally 
agreed that the foundations of scientific knowledge cannot be 
settled, or even verified, by the normal processes of science itself. 
If such questions are asked as, what is the status of a scientific 
theory? or, what is the meaning of the word "explanation" in 
science? or, to what extent is science a logical structure? they 
cannot be answered without transcending the framework of 
science. The scientist must have some idea, which is essentially 
philosophical, of how he is going to set about acquiring an 
understanding of nature before he can apply himself to this task. 
He may in practice be entirely uninterested in philosophy, pre- 
ferring to regard himself as a compiler of demonstrable facts; 
nevertheless, he cannot escape the implications of adopting a 
definite scientific method, which teaches him to record particular 
kinds of facts, by using certain recognized procedures. Thus the 
nature of science in different periods has been determined by the 
methods employed in collecting facts and reasoning about them, 
and by the prevailing approach to the study of natural pheno- 
mena. For example, when the mechanistic philosophy of the 
seventeenth century replaced the teleological outlook of earlier 
times the change in the character of scientific explanation was 
profound: it was no longer sufficient to ascribe the pattern of 
events to divine purpose or the necessary conditions for human 


Consequently, when comparing the scientific achievements of 
one epoch with those of another, it must be recognized that the 
aims and methods of scientific activity may themselves vary. The 
fundamental philosophy of science is neither fixed, nor static, nor 
inevitable. It cannot be claimed that any scientific method is 
correct, without considering the nature of the objects it seeks to 
achieve. Both may be subjected to criticism, for it may be asked 
whether scientists have the proper aims, or whether they are using 
fit methods; and, indeed, from the thirteenth to the seventeenth 
centuries there was continuous and effective criticism of science 
from each of these points of view. During the eighteenth and 
nineteenth centuries, however, there was a tendency for practising 
scientists to feel a confident complacency concerning their aims 
and methods, and to envelop themselves in an impenetrable 
detachment from any attempt to interpret their activities philo- 
sophically. They were scientists, devoted to a peculiarly rigorous 
pursuit of knowledge, not natural philosophers. They despised 
metaphysics and logic. Their limited outlook, and their often 
shallow pragmatism, would have been intolerable to the Greek 
founders of scientific method. 

In essence, the Greek notion of scientific explanation (passing 
into the European tradition through the medieval dependence on 
the philosophy of antiquity) did not differ from that of modern 
science. When a phenomenon had been accurately described so 
that its characteristics were known, it was explained by relating 
it to the series of general or universal truths. The most important 
distinction between Hellenistic science (including that of the 
middle ages) and modern science is in the constitution of these 
universals, and the methods of recognizing them with certainty. 
For Platonists the universal truths were Ideas, the principal task 
of their philosophy it cannot properly be called science being 
the elucidation of the ideal world of perfect Forms of which the 
tangible world was a clumsy model framed in imperfect matter. 
Aristoteleans, on the other hand, denied the separability of Idea 
(or Form) and Matter (or Substance), but nevertheless were 
concerned with the processes by which Forms, the generalizations 
of their science, were detected in the materials provided by sense- 
perception. Phenomena were then explained by comprehending 
them within the a priori scheme of Forms. This procedure required, 
not additions to the already bewildering variety of fact, but the 


exercise of reason upon the facts requiring organization; thus in 
the Physics, for example, proceeding from the known facts of 
motion and change, Aristotle discusses the logical meaning to be 
attached to the idea " motion/ 5 and then from the idea of motion 
deduces the properties of moving things. In this method experience 
and observation are adduced, less to provide bricks to construct 
the fabric of the argument, than to give examples of the author's 
meaning. As Aristotle declares in the opening of the Physics: 
'Plainly in the science of Nature, as in other branches of study, 
our first task will be to try to determine what relates to its first 
principles,' principles however whose validity was tested by the 
rule of reason not that of experiment. As when (to cite the Physics 
once more) he denies the existence of a vacuum on the ground 
that bodies would move in it at an infinite speed, he makes use of 
the logical impossibility of a body being in two places at the same 
time. Aristotle derived his universal truths before the application 
of intensive inquiry to the phenomena themselves, a procedure 
which Francis Bacon contrasted with his own inductive method: 

There are two ways, and can only be two, of seeking and finding 
truth. The one, from sense and reason, takes a flight to the most 
general axioms, and from these principles and their truth, settled 
once for all, invents and judges of all intermediate axioms. The other 
method collects axioms from sense and particulars, ascending con- 
tinuously and by degrees so that in the end it arrives at the most 
general axioms. This latter is the only true one, but never hitherto 
tried. 1 

In building up a body of scientific knowledge other series of 
steps than those of Aristotle were used by the Greeks. One was 
a logical process, akin to that of mathematics, applied where 
mathematical analysis of the phenomena was feasible. This began 
with a series of axioms or postulates, defining the conditions of 
equilibrium in statics, or the geometrical character of the propa- 
gation of light in optics, then deduced the consequences of these 
axioms in the same way that the Euclidean geometry of space is 
deduced from definitions of point and line. The validity of the 
postulates was purely experiential, not deriving from any more 
fundamental truths, so that should it be found, for instance, that 
equilibrium could be produced in other conditions than those 

1 Novum Organum, Bk. I, xix. 


envisaged the science of statics would be false or incomplete; and 
in the same way the validity of their consequences might be 
illustrated from experience. Other Greek writers, notably the 
successors of Aristotle at the Lycaeum, founded their doctrines 
firmly on a discussion of experimental data a method which 
Aristotle had used in his biological works. 1 A large group of later 
Greek scientists were far from merely speculative in their interests 
and confined themselves strictly to the discussion of facts, which 
they sought to extend and enrich by experiment and observation. 
In this way "the sciences," to contrast them with natural philo- 
sophy, came into existence. But their works, though permitting 
quantitative comparisons with experience (as in Ptolemy's 
astronomy), were fragmentary in scope and did not combine into 
a systematic interpretation of the universe as a whole. For this 
the middle ages turned to the Aristotle of the Physics and On the 

As a consequence of his authority the universal truths of 
Peripatetic science, originally formulated by sorting out and 
abstracting with the aid of logic the confused information im- 
parted by sense-perception, tended to become the unquestionable 
arbiters of thought. However, though the attempt to rationalize 
the phenomena of nature by reference to them might often be 
productive of nothing more than intricate mental gymnastics, it 
could occasionally lead to a more factual inquiry. Nor were "the 
sciences" of the later Greeks wholly neglected by a line of the 
more critical and heterodox medieval philosophers. Thus arose a 
problem of method: how were the fruits of the mathematico- 
logical or experiential procedures in investigating nature to 
be reconciled with the knowledge gained by deduction from 
Aristotle's universals? How did knowledge of a phenomenon, in 
terms of its relationship to Aristotle's theory of nature, differ from 
knowledge of the same thing in terms of the complete description 
of the chain of events producing it? The interest of such questions 
was doubtless heightened by the technological progress of the 
middle ages, which literary men did not disregard. There was 
much new knowledge to be systematized (in the field of chemistry, 
for example), new properties of bodies like magnetism to be 
explored. And though the main medieval opinion echoed Plato 

1 On Strato, of. Benjamin Farrington, Greek Science (Penguin Edn., vol. II, 
pp. 27-44). 


and Aristotle in its definition of knowledge as " understanding " 
(passive knowledge) rather than "power to control" (active 
knowledge), a minority foreshadowed a less contemplative, more 
practical view of science. Yet the evidence for actual experimenta- 
tion by medieval philosophers is not massive, even in optics, and 
some of the warmest advocates of the experimental method, like 
Roger Bacon, were guilty of misstatements of fact which the most 
trifling experiment would have corrected. More successfully, they 
discussed the intellectual problem of the relationship between 
facts and theories, modifying Aristotle's teaching with regard to 
the acquisition of knowledge, the nature of causation, and the 
character of the proof of a proposition. It has been suggested that 
the middle ages witnessed the philosophical development of the 
experimental method, through whose systematic application the 
dramatic changes of the scientific revolution were effected. 1 
Attention has been drawn to the empiricism of such philosophers 
as William of Ockham, who regarded as "real" only that which 
could be perceived by sensation, and to the notion of explaining 
an event by giving a history of its antecedents, among other signs 
of the future onslaught upon the foundations of Aristotelean 
physics. But traditional ideas continued to satisfy the majority 
until the seventeenth century, and the philosophic conception of 
empiricism was a very different thing from its application to 
scientific problems. 

No important re-statement of scientific method was made 
during the sixteenth century. The medieval tradition continued 
to run strong, yielding wider divagations from Peripatetic ortho- 
doxy in Leonardo or Copernicus, or the philosophers Cardan and 
Telesio, but there was no philosopher independent enough to 
transfer the weight of scientific authority to completely new bases. 
Instead, it may be noticed that a number of the more interesting 
developments in the science of the period signify that science was 
outgrowing its cradle, philosophy. They bear the mark of the 
practical hand of a Vesalius or an Agricola. Since no true science 
can remain permanently at the level of simple description, the 
first half of the seventeenth century witnessed further efforts at 

1 e.g., A. C. Crombie: From Augustine to Galileo (London, 1952), p. 217, 
etc.: 'The development of the inductive side of natural science, and in fact the 
thorough-going conception of natural science as a matter of experiment as 
well as of mathematics, may well be considered the chief advance made by the 
Latin Christians over the Greeks and Arabs.' 


rationalization. Of these two were properly philosophic and 
systematic: Francis Bacon aimed at an exclusively experiential 
method of scientific inquiry, while Descartes fabricated a new 
logical key to nature. The third was Galileo's conscious reforma- 
tion of the processes of scientific reasoning in mechanics, which was 
less a philosophy of science applied to the solving of particular 
problems than a reconstruction of a department of science which 
necessitated the introduction of far-reaching philosophic principles. 
The types of question which a scientist may ask which the 
method he uses enables him to formulate, and possibly to solve 
may of course be infinitely varied. But here it is useful to single 
out two groups among them. The first kind may begin with such 
words as "How can we demonstrate that . . .", "How may it be 
proved that . . .". These questions are defined, for the investigator 
has an idea, however vague, and seeks to test it. The second kind 
are undefined, taking such a form as "What are the factors in- 
volved in . . .", "What is the relationship between . . .", "What 
are the facts bearing upon . . .". Here the investigator has hardly 
arrived at the stage of ascertaining and ordering the relevant facts, 
much less examining a hypothesis. Copernicus' problem falls into 
the first of these groups, and the problems of seventeenth-century 
chemistry and physiology into the second. Part of Bacon's signifi- 
cance in the history of science resides in his realization of the 
insufficiency of the first aspect of scientific method alone, and 
though he made a notable contribution towards it, the second 
aspect attracted his main interest. He found the theory of scien- 
tific explanation that he encountered insufficient, partly perhaps 
because his education in renaissance humanism gave him little 
acquaintance with the natural philosophers of the late middle 
ages; but still more warmly, he condemned inattention to the 
methods by which the range of scientific facts could be enlarged, 
or the facts themselves tested and more closely knit together. It 
was one of his favourite themes that for many centuries genuine 
contributions to solid knowledge had been the work of artisans 
rather than of philosophers, of the weavers of speculation. Bacon's 
writings have often been described as though his criticisms and 
proposals were directly and solely the result of his social sense; as 
though, because he believed that progress in material civilization 
was a worthy end (a belief shared by both Galileo and Descartes), 
he reasoned that the single function of science was to enhance 


man's command over natural forces. He has thus been depicted 
as the first philosopher to appreciate the potentialities of science 
as the servant of industrial progress. The truth seems to be rather 
more complex. It is not even true that Bacon was the first to see 
science as a powerful agent in improving material welfare, for this 
point had been made by the empiricists of the middle ages and was 
part of the common descent of magic and science. Nor was Bacon 
merely a philosophical technologist; if he wrote 

the true and lawful goal of the sciences is none other than this: that 
human life be endowed with new discoveries and power, 

he also declared, more emphatically, that as 

the beholding of the light is itself a more excellent and a fairer thing 
than all the uses of it so assuredly the very contemplation of things 
as they are, without superstition or imposture, error or confusion, is 
in itself more worthy than all the fruit of inventions . . . we must 
from experience of every kind first endeavour to discover true causes 
and axioms, and seek for experiments of Light, not for experiments of 
Fruit. 1 

Many passages in Bacon's writings indicate that he had a philo- 
sophic appreciation of the value of knowledge for its own sake, 
not merely for its utilitarian applications. The test by works, in 
Bacon's thought, assumed a particular importance not because 
works were the main end of science, but rather because they 
guaranteed the rectitude of the method used. A discovery or 
explanation which was barren of works could hold no positive 
merit not because it was useless to man, but because it lacked 
contact with reality and possibility of demonstration. Since 
Bacon's science was to deal with real things, its fruits must be real 
and perceptible. 

Measured by these standards, Aristotelean science was a hol- 
low structure, dealing with abstractions rather than real things, 
justified by no fertility in works. Bacon did not deny that there 
was truth in the content of orthodox science he was quite as 
certain as Aristotle of the stability of the earth but these truths 
were buried in a misleading and sterile philosophy. His remedy 
was to return to a consideration of the bare facts, and above all 
to increase vastly the range of facts available. Only when all the 

1 Novum Organum, Bk. I, Ixxxi, cxxix, Ixx. 


material upon a particular phenomenon, or natural process, had 
been collected, classified and tabulated could any general con- 
clusions be drawn from it and generalizations be framed. The 
facts might be collected from experience, from reliable reports, 
from the lore of craftsmen, but above all from designed experi- 
ment. For Bacon clearly conceived of experiment not merely as a 
trial "to see what happens," but as a way of answering specific 
questions. The task of an investigator was to propose questions 
capable of an experimental answer, which could then be recorded 
as a new fact appertaining to the phenomenon under study. In 
this way the lists of "instances" were to be built up, as Bacon 
attempted himself to construct tables of instances of heat and 
motion. Other aids were then required in the intellectual process 
of finding order in the mass of fact compiled, for which also Bacon 
made suggestions. In the New Atlantis the work of the fact-gatherers 
is separated altogether from the work of the fact-interpreters, and 
this has been criticized as a defect in Bacon's system. Yet in 
practice in science it has often happened that a new generaliza- 
tion in theory has interpreted a mass of evidence assembled by a 
line of earlier experimental investigators. 

Some comments on science have denied categorically that there 
is any such thing as a specific "scientific method," by saying, for 
example, that science is organized common sense. Bacon's method 
at least seems to suffer from excessive formalization and a top- 
heavy logical apparatus. Even in his own ventures into scientific 
research Bacon did not observe his complex rules very strictly, 
and hence the once popular notion that he invented and described 
the method of experimental science is no longer acceptable. 
Modern science was not consciously modelled upon Bacon's 
system. Mathematical reasoning especially, so freely and success- 
fully exploited from the earliest stages of the scientific revolution, 
he never understood so that its essential role was hidden from 
him. It has also been said, with less justice, that the integration 
of theory and experiment typical of modern research was not 
allowed for in his system and that he did not foresee the importance 
of hypothesis in the conduct of an investigation. In fact Bacon did 
envisage the situation where reflection on the facts suggests 
several possible theories, and discussed the procedure to be 
adopted for the isolation of the correct one by falsification of the 
others. And certainly he understood the decisive nature of a 


" crucial experiment" in judging the merit of an idea taking shape 
in the investigator's mind. It should not be forgotten, too, that 
pure fact-collection (the first stage in Bacon's system) has been a 
most important fraction of all scientific work up to the present 
time. Even the routine verification of measurements, or the 
establishment of precise constants, has been productive of original 
discoveries. It is true that the main course of physical science in 
the seventeenth century ran in a very different direction, that 
in the new mechanics of Galileo the plodding fact-gathering 
imagined by Bacon had little significance; elsewhere in science, 
however, where the organization of ideas was less advanced and 
the material far more complex and subtle, the straightforward 
acquisition of accurate information was a more fruitful endeavour 
than premature efforts at conceptualization. This is most 
clearly true of the biological sciences; no Galileo could have 
defined the strategic ideas of geology or physiology which only 
emerged from the wider and deeper knowledge of facts obtained 
in the nineteenth century. Bacon's advice that solid facts, certified 
by experiment, should be collected and recorded was sound and 
practical; this task occupied chemistry and biology till towards the 
end of the next century. But in the long run the great generaliza- 
tions in these fields did not follow from the kind of digestion and 
sublimation of fact that Bacon had described. 

While Bacon's works gave a useful impetus to the growing 
interest in science, especially in England, his attempt to define 
the intellectual processes involved in the understanding of nature 
was limited and only partially helpful. Empiricism alone is an 
insufficient instrument in science. The history of the scientific 
revolution shows the fertility of the critical examination of con- 
cepts and theories, even when the modification of the simple 
account of the facts is insignificant (as with Galileo's new concepts 
of inertia and acceleration) . Bacon's views were characterized by 
his approach to science, which was that of a philosopher rather 
than that of an experienced investigator. His own ventures in 
research are notoriously uninteresting and unproductive, for 
except in his leaning towards an atomistic materialism he was out 
of sympathy with the progressive ideas of the time, and remarkably 
indifferent to those developments which posterity has found most 
significant. His logical system was for the most part ignored by 
those who were finding how to make discoveries regardless of 


logical systems, and consequently modern science did not so much 
grow up through Bacon as around him. 

Galileo offers a very different picture. On the one hand he was 
mainly occupied with purely scientific matters and the discussion 
of specific problems. He did not construct a methodical philosophy 
of science, though the elements of such a philosophy may be 
extracted from his works. On the other hand he may properly be 
described as a philosopher, for his conscious reflection on the 
obstructions to be overcome in arriving at a clear and confident 
understanding of nature is explicit in a number of passages and 
implicitly conditions the revolution in ideas that he effected. Like 
other major critics of Aristotle, Galileo was faced with two 
inescapable problems: on what foundations was the intellectual 
structure of science to be built, and what criteria of a satisfactory 
explanation were to replace those of Aristotle? With Galileo these 
questions were not answered in prolonged metaphysical or logical 
analyses though it seems clear that his ideas were shaped by just 
such analyses carried out by his predecessors but the answers 
were given as they became necessary in the progress of his attack 
on the prevailing ideas of nature. As scientist Galileo's aim might 
be to detect Aristotle's errors in fact or reason, while as philo- 
sopher he demonstrated more fundamentally how these errors had 
arisen from weaknesses in method that were to be avoided by 
taking a different course. The negative exposure of an isolated 
mistake by means of experiment or measurement was not, in 
Galileo's view, the sole advance of which the new philosophy was 

Galileo's two greatest treatises are polemics. They do not relate 
how certain conclusions were reached, instead they seek to prove 
that these conclusions are certainly true. Their arguments are 
therefore synthetic, and the texture of reasoning and experience 
is so woven that experience appears less as a peg upon which a 
deduction depends, than as an ocular witness to its validity. It is 
universally the case that the methods by which a discovery is 
made and expounded differ, in varying degrees, and Galileo 
rarely used the direct technique of reporting and inference, so 
much favoured later by the English empiricists. In the Dialogues 
and Discourses the foundations of scientific knowledge are shown to 
reside in phenomena and axioms conjointly. By its attention to 
actual phenomena Galilean science was made real and experien- 


rial; by its use of the capacity of the mind to apprehend axiomatic 
truths its logic was made analogous to that of mathematics. The 
latter were indeed generalized from the former, but the process 
might involve historical as well as philosophical elements. Thus 
a fundamental axiom of the Dialogues is that heavenly bodies 
participate in uniform circular motion, while in the Discourses 
successive propositions in dynamics are deduced from the axio- 
matic definition of uniform acceleration. Such axioms, illustrated 
and confirmed by experiment, become the starting-point for 
arguments through which their implications are unfolded (in the 
manner of Euclidean geometry or Archimedean statics) and again 
in turn verified by experience, or applied to specific problems, 
such as the isochronism of the pendulum. 

Galileo's remarks on the procedure to be adopted in arriving at 
these principal generalizations are therefore of special interest. 
The most important step is that of abstraction. The essential 
generalizations are not to be taken as the end-product of the 
logical examination of an idea, in the manner of Aristotle, but 
are obtained by abstracting everything but the universal element 
in a particular phenomenon, or class. So far Galileo agrees with 
Bacon, though he offered no comparable set of logical rules for 
effecting this operation. He went on, however, to insist emphati- 
cally that by abstraction it is learnt that the real properties of 
bodies are purely physical, that is, size, shape, motion, propin- 
quity, etc., not colour, taste or smell so that as he stated in the 
Saggiatore, the " accidents, affections and qualities" attributed to 
them are not inherent in the bodies at all, but are names given to 
sensations stimulated in the observer by the physical constitution 
of that which he perceives. Galileo noted that this failure to ab- 
stract from sensations to the underlying physical reality had given 
rise to much confusion in the study of heat; physically considered 
(he says) there is no mystery in heat, which is merely a name 
applied to a sensation produced by the motion of a multitude of 
small corpuscles, having a certain shape and velocity, whose 
penetrations into the substance of the human body arouse such 
sensation. 1 In these opinions the influence of Epicurean atomism 
is evident; one might say that this whole approach to the question 

1 // Saggiatore (Bologna, 1655), PP- I 5~3- Bacon also agreed that 'heat is 
an expansive motion restrained, and striving to exert itself in the smaller 
particles.' (Novum Organum, Bk. II, xx.) 


of primary and secondary qualities is determined by a mechanistic 
notion of the composition of matter. The explanation of a scientific 
problem is truly begun when it is reduced to its basic terms of 
matter and motion the transformation which remained the ideal 
of classical physics. The name heat could not be a cause, since as 
Galileo pointed out there is nothing between the physical pro- 
perties of bodies with the varying motions and sizes of their com- 
ponent particles and the subjective perceptions of the observer. 
He found other instances in conventional science of this tendency 
to believe that matters could be explained by juggling with 
abstract names, as when in the Dialogues gravity is defined as only 
the name of that which causes heavy bodies to fall; naming does 
not contribute to understanding. Of course Galileo did not mean 
that there is no purpose in classifying phenomena; his argument 
is that classifications based on superficial characteristics and naive 
analyses are misleading because they conceal physical realities. 
They had concealed the universal generalizations on motion, 
whether caused by gravity or any other force, which it was 
Galileo's main achievement to reveal. 1 

( In the process of abstraction an important aid was mathematics. 
If the elements of a problem were capable of statement in numeri- 
cal terms then the most exact definition had been framed and the 
most general case considered. Moreover, by transposition into 
mathematical language the conditions of the problem could be 
exactly prescribed, in order to remove the imperfections and 
minor variations that always occur in actual experience. As in 
geometry the areas of triangles can be calculated more precisely 
than they can be measured, so in mechanics the properties of the 
lever, the inclined plane, the rolling sphere could be calculated 
by reducing these physical bodies to geometrical forms whose 
behaviour could be established by abstraction from that of their 
physical counterparts. Galileo knew that this was a function of the 
imagination; a calculus may solve a problem, but the due con- 
ditions must be postulated before the calculation can begin. The 
motion of a perfect sphere on a perfect plane must be inferred 
imaginatively from the motion of physical spheres on physical 
planes, or the motion of an ideal pendulum from that of actual 

1 Similarly, a chief problem of the early botanical taxonomists was to 
penetrate below the superficial differences and similarities in plants to more 
"real" morphological distinctions. 


oscillating bodies, but this, for Galileo, was strictly analogous to 
Euclid's abstraction in the definition of space, or Archimedes' 
assuming that the cords hanging from the ends of a balance are 
geometrically parallel. Mathematics, serving as a guide to the 
imagination as well as handling the abstracted properties, could 
yield further statements which, through reference to experience, 
might confirm the process of abstraction and the generalizations 
derived from it. In this ideal world of abstraction, without 
resistance or friction, in which bodies were perfectly smooth and 
planes infinite, where gravity was always a strictly perpendicular 
force and projectiles described the most exquisitely exact para- 
bolas, the principles of Euclidean geometry held absolutely. The 
world of Galileo's imagination in mechanics was in fact Euclid's 
geometrical space with the addition of mass (later defined pre- 
cisely by Newton), motion and gravity. The secret of science, in 
Galileo's outlook, was to transfer a problem, properly defined, to 
this abstracted physical universe of science which, as ever greater 
complexities are added to it, approximates more and more closely 
to the actual universe. For the architecture of the real world is no 
less mathematical than that of Euclidean space, the book of nature 
being written 'in mathematical language . . . the letters [being] 
triangles, circles and other geometrical figures, without which 
means it is humanly impossible to comprehend a single word.' 
As Galileo elsewhere declared, there is no distinction between 
"real truth" and mathematical truth. On this account he has 
been called a Platonist, whereas perhaps he was rather a Euclidean 
in mechanics, never cultivating the mathematical mysticism that 
distinguished Kepler. Moreover, Galileo recognized that while 
mathematical logic is infallible, it may rest on false assumptions, 
like those of the Ptolemaic system, which e although it satisfied an 
Astronomer meerly Arithmetical, yet it did not afford satisfaction to 
the Astronomer Phylososphical* It was but too easy to mistake one of 
nature's circles for a triangle. 

By the method of abstraction, moreover, the scientific concept 
of " laws of nature" was simply and neatly accommodated. This 
concept, unknown both to the ancient world and to the Far 
Eastern peoples, seems to have arisen from a peculiar interaction 
between the religious, philosophic and legalistic ideas of the 
medieval European worldjjlj, is apparently related to the concept 
of natural law in the social and moral senses familiar to medieval 


jurists, and signifies a notable departure from the Greek attitude 
to nature. The use of the word "law" in such contexts would 
have been unintelligible in antiquity, whereas the Hebraic and 
Christian belief in a deity who was at once Creator and Law-giver 
rendered it valid. The existence of laws of nature was a necessary 
consequence of design in nature, for how otherwise could the 
integrity of the design be perpetuated? Man alone had been given 
free-will, the power to transgress the laws he was required to 
observe; the planets had not been granted power to deviate from 
their orbits. Hence the regularity of the planetary motions, for 
example, ascribed by Aristotle to the surveillance of intelligences, 
could be accounted for as obedience to the divine decrees. The 
Creator had endowed matter, plants and animals with certain 
unchangeable properties and characteristics, of which the most 
universal constituted the laws of nature, discernible by human 
reason. This conception is clearly capable of association with a 
mechanistic philosophy, and irreconcilable with animism; as 
Boyle put it: 

God established those rules of motion, and that order amongst things 
corporeal, which we call the laws of nature. Thus, the universe being 
once framed by God, and the laws of motion settled, the [mechanical] 
philosophy teaches that the phenomena of the world are physically 
produced by the mechanical properties of the parts of matter. 1 

If this transcendental status be granted to the laws of nature 
so that one may inquire what they arc, but not why they hold 
the question may still be asked, "How may a given proposition 
be recognized as a law of nature? " In other words, how gloes a law 
of nature differ from any other generalization which happens to 
be true because no instance to the contrary has yet been dis- 
covered? Modern philosophers of science, having deprived the 
laws of nature of their transcendental status, present their own 
answers to this problem. Galileo, and after him Newton, obtained 
an answer to it by application of the method of abstraction. When 
Galileo created by abstraction the essential model of the pheno- 
mena of motion which he studied, he transformed the pragmatic 
validity of a generalization appropriate to the world of experience 
into the absolute validity of the law of nature in the intellectual 

1 The Excellence and Grounds of the Mechanical Philosophy ', in Philosophical Works, 
abridged by Peter Shaw (London, 1725), vol. I, p. 187 (condensed). 


model. Thus Newton, following Galileo, formulated his laws of 
motion as laws of nature having complete applicability within the 
fabric of mathematical physics, whose conclusions as a whole can 
be confirmed by direct observation. In this way the difficulty that 
the perfect universality of the laws of nature cannot be established 
by experience of countless instances was overcome. For Galileo 
and the later scientists who adopted his method such laws had a 
greater force than descriptive generalizations could attain, because 
they had acquired a fundamental systematic status in the scientific 
picture of the universe. 

Hence laws of nature could be considered in theory as being 
rigorously exact, although the ascertainable correspondence be- 
tween laws and experience in the physical world is limited by 
probability-factors in experiments and by the intervention of a 
multitude of complications. Such limitations were discovered, for 
example, by the early experimenters in mechanics who discovered 
that Galileo's theorems on motion could not be rigorously con- 
firmed when applied to the movements of physical bodies. Galileo 
had clearly appreciated the exceptional usefulness of the concept 
of laws of nature in which they were taken to represent that which 
the intellect, aided by scientific abstraction, conceives as the 
essence of certain phenomena, but it fell to others to demonstrate 
more satisfactorily the precautions which the scientist must take 
in relating the laws to the crude evidence of the senses. 

When abstraction has played its part, when attention has been 
given to the really existing physical properties of bodies, when the 
mathematization of the phenomena has been fully explored and 
a theoretical science begins to take shape, how is the investigator 
to determine whether his image or model of things in the ab- 
stracted universe represents faithfully things as they are according 
to experience? Galileo's answer to this problem, prepared for him 
by earlier logicians, was the appeal to experiment. If theoretical 
examination suggests that in specified conditions the event B will 
follow the event A, then the reasoning can be tested by creating 
those conditions, and making the observation. This doctrine is not 
explicit in Galileo's writings, but it is implicit in their texture. 
Thus the difference between Galileo and Bacon in this respect is 
that the former emphasized mainly the role of experiment in test- 
ing a theory, or determining its constants, while the latter stressed 
the role of experiment as a means of obtaining information. In 


Galileo's view the questions which the investigator can ask nature 
are most useful when they are not random questions, but are so 
designed that a single unambiguous response can be elicited from 
the experiment. This is probably the cardinal feature of modern 
scientific method, of which numerous examples are to be found in 
Galileo's writings, such as the use of the experiment with the in- 
clined plane to verify the law of acceleration. It would be erroneous 
to suppose that it had never appeared in earlier scientific research, 
but it is with Galileo that it becomes its main pillar. It must be 
observed, however, that the experimental method is capable of 
bearing different connotations. With Bacon the appeal to experi- 
ment is a remedy for ignorance: 

Let further inquiry be made as to the comparative heat in different 
parts and limbs of the same animal; for milk, blood, seed and eggs 
are moderately warm, and less hot than the outward flesh of the 
animal when in motion or agitated. The degree of heat of the 
brain, stomach, heart, and the rest has not yet been equally well 
investigated. 1 

With Galileo experiment is a test of knowledge, confirming a 
necessary deduction in the development of a sound theory, so that 
he can even declare: " If you were to perform such an experi- 
ment then you would obtain such a result," although he has never 
made the experiment himself. Or in other passages he refers to 
his readers' experience of the reflection of light from mirrors, the 
motion of bodies in a ship under way, the passage of fluids between 
vessels; a possible experiment is described, but none is reported 
circumstantially. The function of these " thought-experiments" 
in the argument of the Dialogues or Discourses is not to demonstrate 
a new fact so much as to guide the imagination into perceiving the 
agreement between experience and the ideas put forward. As 
Galileo had framed his concepts, not in the laboratory but by a 
correct analysis of the common evidences of motion, so in exposition 
reversing the process he teaches the reader to analyse his own ex- 
perience of motion by means of these thought-experiments. He 
was well aware that experimentation is a double-edged weapon, 
deceiving those who use it crudely, as when he writes of the 
"sublime wit" of Copernicus, who 

did constantly continue to affirm (being perswaded thereto by reason) 
that which sensible experiments seemed to contradict; for I cannot 
1 Novum Organum, Bk. II, xiii. 


cease to wonder that he should constantly persist in saying, that 
Venus revolveth about the Sun, and is more than six times further 
from us at one time, than at another; and also seemeth to be alwayes 
of equal bigness, although it ought to shew forty times bigger when 
nearest to us, than when farthest off. 1 

Sheer empiricism, therefore, could not uncover physical reality, 
which could only be glimpsed through the alliance of analytical 
reasoning (especially of the mathematical kind), scientific imagina- 
tion, and experimental caution. 

From the critique of empiricism it emerges that in Galilean 
science experiment is incompetent to confirm the whole intellectual 
structure, whose conceptual elements transcend experiment. For 
example, the concept of acceleration which science owes to Galileo 
cannot be proved in the laboratory, though its applicability in 
representing phenomena can be illustrated. For the definition of 
acceleration involves the further concepts of time and velocity, the 
latter a function of time and the concept distance. There is perio- 
dicity in nature, and there are intervals in nature, but nature offers 
no ready-made dimension-theory embracing the concepts of time 
and distance. These can have no other status than that of ideas or 
mental constructs which help to form the world-picture, having 
the advantage that unlike concepts of beauty and justice they can 
be understood in the same sense by all men. But their definition is 
of mind, not innate in the fabric of the universe. The concept time 
gives order to certain kinds of experience, the concept distance to 
others, and from these arise velocity and acceleration rationalizing 
others still, so that the first test^br a definition of acceleration must 
be its assimilability in logic to existing dimension-theory; more- 
over, in a second test, by experiment, the usefulness of the new 
construct cannot be distinguished from the usefulness of the exist- 
ing constructs, time and distance, so that effectively the whole 
system of constructs must be tested together, if at all. Though the 
Galilean scientist seeks to penetrate ever deeper into physical 
reality, the nodes of his exposition of nature can never be more 
than mental constructs, time, acceleration, the chemical element, 
or the electron, which give order and significance to the experi- 
mental data. This incidentally provides the justification for 
Galileo's thought-experiments; the constructs are equally valid 
when they give order to the facts of experience, duly analysed, as 
1 Dialogues (trans. T. Salusbury), p. 306. 


when they apply to the most delicate determinations of the 

If the theoretical part of science, leaving aside its practical 
success in operating with materials and instruments, is a frame- 
work of mental constructs giving order to experience, then it 
follows that the only kind of explanation that is possible is one 
that arranges the constructs in a logical pattern; as when the 
properties of the molecule are traced to its atomic structure, and 
the properties of the atom to its electrons. The sole method of 
assigning a cause to any particular phenomena is to invoke the 
constructs applicable to it, that is, the generalizations derived 
from the study of less complex phenomena. In this way Galileo 
used his concepts of motion to describe and account for the tra- 
jectory of a projectile, as a modern physiologist more elaborately 
uses the concepts of cytology, biochemistry and even the physical 
notions of matter and energy to describe and account for the 
functioning of a part of the body. That it is never possible to touch 
any cause more fundamental than a construct or generalization 
derived from the description of some definite phenomenon, and 
that therefore explanation and description have no really distinct 
significance in science, was the great methodological discovery upon 
which the scientific revolution flourished. In Galileo's works its 
full powers appear for the first time, but it was only gradually 
extended from mechanics to the non-physical sciences. In the Dis- 
courses (Third Day) Galileo disposed of the causes of the accelera- 
tion of freely falling bodies imagined by philosophers as fantasies 
unworthy of examination: 'At present it is the purpose of our 
Author merely to investigate and to demonstrate some of the 
properties of accelerated motion (whatever the cause of this 
acceleration may be).' This does not mean that in replacing the 
question why by the question how Galileo has excluded the study 
of phenomena in terms of cause and effect it was his pupil 
Torricelli who proved that the cause of the horror vacui (so called) 
was the pressure of the air. Mere simple description, like that of 
anatomy, was not the sole end of the new sciences Galileo created, 
for the formulation of constructs and generalizations is a necessary 
feature of the full description of a class of events, e.g. accelerated 
motion. Galileo seems rather to be making the minor point that 
if the cause of B is called A, the first subject of study must be B 
itself (since it is from B that the very existence of A is wholly or 


in part inferred), and the more serious point that to describe and 
account for the A-B relationship, the investigator must be able to 
make a number of statements concerning A independently of B 
in order to establish its character. In other words, since causation 
and full description are synonymous, the "cause" of B (accelera- 
tion) is a property of A (gravity), not of B, and can be sought only 
in the description of A. This is Galileo's attitude throughout the 
Discourses, as it is Newton's throughout the Principia. The explana- 
tion of phenomena at one level is the description of phenomena at 
a more fundamental level, that is, one nearer to the primary 
realities of classical physics, matter and motion. 

Following the example of Galileo, the scientist may as it were 
work either upwards or downwards; he may seek for a more 
fundamental construct (like the law of inertia, or the laws of 
thermodynamics) or he may examine the applications of the con- 
struct to the details of a complex phenomenon (like the isochron- 
ism of the pendulum). In either case he may have to handle 
constructs which are not reducible to the ultimate physical reali- 
ties, as was the case for instance with Newtonian mechanics where 
the law of gravitation had to be taken as descriptively correct, 
though gravity was not explicable in terms of matter and motion. 
For Galileo there was no anomaly in recognizing that certain 
constituents of the physical world had to be accepted as axio- 
matic; descriptive analysis can only advance gradually from the 
coarse to the refined, from the lower to the upper levels, each with 
its appropriate generalizations. In the period between Galileo and 
Newton, however, the validity of the purely descriptive generaliza- 
tion (which rests upon scepticism concerning the possibility of 
arriving at a final indubitable truth serving as the single origin of 
scientific thought) was challenged in the philosophy of Descartes, 
and rejected by the systematists who expounded Cartesian ideas. 
The chief difference between Galileo and Descartes lay in this, 
that while the former believed that a body of knowledge successful 
in organizing sense-perceptions (duly refined and analysed) and 
in framing generalizations based on them gave an adequate under- 
standing of nature, the latter believed that there was no reliable 
test of the significance of sense-perceptions other than that which 
issues from a deeper metaphysical certainty. The mind, being 
extra-nature, was capable of doubting anything external to itself 
in nature. 



\As Descartes relates in the Discourse on Method (1637), after 
completing a thorough education, in which, ' not contented with 
the sciences actually taught us) I had read all the books that had 
fallen into my hands, treating of such branches as are esteemed 
the most curious and rare, '(he found himself involved in many 
doubts and errors, persuading him that all his attempts at learning 
had taught him no more than the discovery of his own ignorance. 
In philosophy, despite all the efforts of the most distinguished 
intellects, everything was in dispute and therefore not beyond 
doubt, and as for the other sciences 'inasmuch as these borrow 
their principles from philosophy, 5 he reasoned that nothing solid 
could be built upon such insecure foundations. 

In this perplexity,fbescartes proposed to himself four "laws of 
reasoning" which he applied in the first place to the study of 
mathematics: } 

In this way I believed that I could borrow all that was best both in 
geometrical analysis and in algebra, and correct all the defects of the 
one by the help of the other. And, in point of fact, the accurate ob- 
servance of these few precepts gave me such ease in unravelling all 
the questions embraced in these two sciences, that in the two or three 
months I devoted to their examination, not only did I reach solutions 
of questions I had formerly deemed exceedingly difficult, but even as 
regards questions of the solution of which I remained ignorant, I was 
enabled as it appeared to me, to determine the means whereby, and 
the extent to which, a solution was possible. 

Mathematical ideas, then, could be understood with perfect 
clarity and mathematical demonstrations accepted with absolute 
confidence. These principles, to which Descartes held firm in all 
his scientific activities, ally him with Galileo in the attainment of the 
ideal of mathematization throughout science. Indeed, Descartes' 
most valuable contribution to the scientific revolution was the 
co-ordinate geometry described for the first time in the same 
volume as the Method. But his grasp of a starting point for the 
comprehension of fact, rather than the abstractions of mathe- 
matics, depended upon a form, of psychical crisis from which he 
emerged possessed with the metaphysical force of the statement' 
/ think, therefore I am: 

I thence concluded that I was a substance whose whole essence or 
nature consists in thinking, and which, that it may exist, has no need 
of place, nor is dependent on any material thing; so that "I," that is 


to say the mind by which I am what I am, is wholly distinct from the 
body, and is even more easily known than the latter, and is such, that 
although the latter were not, it would still continue to be all that is. 

This led Descartes to inquire why he had found Cogito, ergo sum 
an infallible proposition, whence he convinced himself that all 
things clearly and distinctly perceived as true, are true, 'only 
observing that there is some difficulty in rightly determining the 
objects which we distinctly perceive.' Further, he declared that 
since the mind is aware of its own imperfection, there must be a 
being, God, which is perfect and that since perfection cannot 
deceive, those ideas which are clearly and distinctly perceived as 
true are so because they proceed from perfect and infinite Being. 
So much more certain are the fruits of reason, says Descartes, that 
we may be less assured of the existence of the physical universe 
itself, than of that of God, 'neither our imagination nor our senses 
can give us assurance of anything unless our understanding 
intervene . . . whether awake or asleep, we ought never to allow 
ourselves to be persuaded of the truth of anything unless on the 
evidence of our reason.' 

After this denunciation of empiricism, this declaration that all 
knowledge of truth is implanted by God, this assertion that the 
task of the scientist is to frame propositions as clearly and distinctly 
true as those of geometry, what suggestions can be made for the 
deciphering of the enigma of nature? According to Descartes, it 
is necessary to follow exactly that procedure which Bacon had 
condemned in Aristotle, that is, to establish the prime generaliza- 
tions that are 'clearly and distinctly true.' 

I have ever remained firm in my original resolution ... to accept 
as true nothing that did not appear to me more clear and certain than 
the demonstrations of the geometers had formerly appeared; and yet 
I venture to state that not only have I found means to satisfy myself 
in a short time in all the principal difficulties which are usually 
treated of in philosophy, but I have also observed certain laws estab- 
lished in nature by God in such a manner, and of which he has im- 
pressed on our minds such notions, that after we have reflected 
sufficiently on these, we cannot doubt that they are accurately 
observed in all that exists or takes place in the world. 

Thus the science of Descartes is a centrifugal system, working 
outwards from the certainty of the existence of mind and God to 
embrace the universal truths or laws of nature detected by reason, 


and then from the "concatenation of these truths" revealing the 
mechanisms involved in particular phenomena. It is systematic, 
unlike the "new philosophy" of Bacon or Galileo, because its aim 
is not to enunciate a correct statement here and there as it becomes 
accessible to intellect, but to provide an unchanging fabric whose 
relevance to particulars is the sole remaining subject of inquiry. 
In this respect, despite his contempt for scholasticism, Descartes 
sought for himself the commanding authority of a new Aristotle. 
Indeed, among Cartesian scientists, and still more among Car- 
tesian philosophers of later generations, a new scholasticism 
flourished through the dissection, embroidering and expansion of 
Descartes' doctrines, until they, like Aristoteleanism in the six- 
teenth and seventeenth centuries, were in turn regarded as a 
bulwark against dangerous innovations and as the philosophic 
justification of religious orthodoxy. 1 

(Apart from his researches in optics and mathematics by far 
the portion of the whole which proved of greatest value to science 
Descartes preferred to express his ideas in the form of a model, 
whether of a man or of the universe. Superficially this procedure 
seems to resemble the Galilean process of abstraction, but in 
reality it is very different. Having settled his principles, Descartes 
believed that to philosophize about mathematical abstractions 
was to promote delusions; his object was the real world, but as he 
did not know from experience what the mechanisms of the real 
world, or the actual human body, are, he was forced to imagine 
what they must be to accord with the principles and such know- 
ledge as he had. He did not claim that in describing the model he 
was describing the real world, only that from the identity of their 
properties the real world could be understood in terms of the 
model. Its mechanism was absolute, since it followed from the 
dualism of mind and matter that all the phenomena of nature 
resulted from the properties of matter, especially its motion, which 
in turn were fixed by natural law. The laws of nature, including 
the definition of matter by extension and the impossibility of a 
vacuum, the law of inertia, and the laws of impact between 
particles, were derived by Descartes as ideas 'clearly and dis- 
tinctly perceived to be true.' Thus Descartes and Galileo agreed 
that the only physical reality which science can study is that of 
matter in motion; unlike Galileo, however, Descartes did not 
1 Cf. A. G. A. Balz: Cartesian Studies (New York, 1951). 


hesitate to extrapolate far beyond the limitations of mathematical 
analysis or experimental inquiry. In the end, elaboration of the 
principles, guided only by the criteria of "clear and distinct/' 
yielded.)) in Cartesian cosmology, chemistry and physiology 
nothing other than subtle scientific fantasy. 

Again, with regard to the functions of experiment Descartes and 
Galileo adopted antithetical positions. The pillars of Cartesian 
science were " clear and distinct" ideas formulated as laws of 
nature; it was to fit these, and not experimental evidence, that its 
subsidiary theories were shaped. It was essentially deductive from 
these natural laws, and if knowledge did not supply the requisite 
materials, then they had to be invented with the aid of reasoned 
deduction, as the celestial vortices carrying the planets about the 
sun, the three kinds of matter and the variously contrived pores 
of substances were invented in accordance with the exigencies of 
experience and reason. Of course, experience was respected in the 
sense that Descartes sought to explain in his model the sum of the 
phenomena of nature as he knew them, for it is obvious that he 
could not have deduced magnetism within his system had he not 
known of its manifestations. But Descartes made no attempt to 
confirm his mechanisms in detail by experiment. The foundations 
of knowledge, he thought, were best settled without it: 

for, at the commencement, it is better to make use only of what is 
spontaneously represented to our senses, and of which we cannot 
remain ignorant, provided we bestow on it any reflection, however 
slight, than to concern ourselves about more uncommon or recondite 
phenomena; the reason for which is, that the more uncommon often 
mislead us so long as the causes of the more ordinary remain 
unknown. . . . 

Experiments indicating some conclusion detached from a deduc- 
tive system Descartes distrusted; hence nothing that Galileo did 
had value for him, because Galileo did not know the cause of 
gravity. This must not be taken to mean that either Descartes or 
his successors were totally blind to the merits of experimentation, 
though it could only be an adjunct when the application of clear 
and distinct ideas failed, or in an obscure inquiry. In his own 
experimental researches Descartes revealed great talent, and those 
who were influenced by him, like the Dutch physicist Christiaan 
Huygens, included some of the great exponents of experimental 
science of the later seventeenth century though indeed they owed 


much less in this respect to Descartes, than to the empirical temper 
of the age, and the emulation of Galileo's example in mechanics. 
It was Huygens who later described Descartes as the author of 
c un beau roman de physique.' Though its doctrines were recited 
into the mid-eighteenth century the Cartesian system of science 
proved sterile, and it may be doubted whether the Cartesian 
philosophy of science ever produced a single useful thought, save 
in the mind of its originator. 1 The optimistic metaphysical belief 
that what is clear and distinct must be true proved unfounded. 
The deductive method, subjected to the destructive criticism of 
the neo-Baconians of the Royal Society, was again convicted of 
fostering works that were shallow, speculative and remote from 
real things. Clearly when Descartes devoted himself to systematics 
his status as a scientist diminished. But the importance of his 
systematic works especially the Principles of Philosophy (1644), the 
text-book of the Cartesian school for nearly a century must not 
be underestimated, for in the mid-seventeenth century the intel- 
lectual appeal of Descartes throughout France, Britain and north- 
western Europe was immensely greater than that of Galileo, while 
Bacon was almost unknown to continental scientists. The very 
fact that Descartes wrote as a philosopher gave his scientific ideas 
greater currency, and to many places where Aristotelean and 
humanistic conventionality lingered untroubled, Cartesian notions 
brought the first breath of a new outlook, a fresh vitality in natural 
philosophy. Thus Oxford, because Descartes was read there, was 
regarded about 1650 as being much in advance of Cambridge. 
His was undoubtedly the pre-eminent intellect in the swelling 
movement, ebullient with ideas and discoveries, that made Paris 
the scientific focus of Europe from about 1630 to 1670. Even 
among those who cannot be enrolled with the expositors of Des- 
cartes' science, there were many who, like Boyle or Newton, 
though they learnt through the use of an empirical or Galilean 
method to criticize his theories, had found in those same theories 
their point of departure; indeed, the main activities in physical 

1 It may be remarked that Descartes' metaphysic of scientific discovery, as 
described in the Method, is essentially individualistic, i.e. it shows how each man 
may learn to frame his own idea of nature. But, just as those sects which claimed 
to be founded on the free interpretation of the Bible imposed the sternest disci- 
pline in order to safeguard the interpretations of their founders, so the later 
Cartesians instead of going through this process of discovery adhered rigidly to 
the idea of nature developed by Descartes himself. 


science for more than a generation after Descartes' death can be 
interpreted, without gross distortion, as a commentary upon 
Descartes' works. And if the Principles of Philosophy proved ephe- 
meral compared with Newton's Mathematical Principles of Natural 
Philosophy even the title suggests a reaction its influence in 
leading later seventeenth-century science to entertain ideas of 
mechanism, of the corpuscular structure of matter, of the im- 
portance of "natural laws," was creative of further progress. 

Perhaps it may justly be said that Descartes' successes in science 
were due less to any peculiar merits in his method, than to his 
native genius for investigation. There is one point, however, both 
in the method and the texture of his thinking on scientific subjects 
that deserves to be singled out. Descartes well understood the 
importance, in any work of research, of scientific imagination, a 
faculty with which he himself was so well endowed that he hardly 
perceived its limitations when controlled by reason alone without 
cautious experimentation. Bacon had recognized that imagination 
or intuition might surmount an inconvenient obstruction; Galileo 
also admitted that in demonstrative sciences a conclusion might 
be known before it could be proved: 

Nor need you question but that Pythagoras a long time before he 
found the demonstration for which he offered the Hecatomb, had 
been certain, that the square of the side subtending the right angle in 
a rectangle triangle, was equal to the square of the other two sides: 
and the certainty of the conclusion conduced not a little to the investi- 
gating of the demonstration. . . , 1 

In Descartes there is a more overt appreciation of the function 
of directed imagination, playing on the problem in hand, in 
formulating hypotheses to be tested by experiment or other means: 

. . . the power of nature is so ample and vast . . . that I have hardly 
observed a single particular effect which I cannot at once recognize as 
capable of being deduced in many different ways from the principles, and 
that my greatest difficulty usually is to discover in which of these 
ways the effect is dependent upon them; for out of this difficulty I 
cannot otherwise extricate myself than by again seeking certain 
experiments, which may be such that their result is not the same 
if it is in one of these ways that we must explain it, as it would 
be if it were to be explained in another. 2 

1 Dialogues (trans. T. Salusbury), p. 38. 

2 Discourse on Method, Part VI; my italics. 


Here experiment is put forward, not as by Bacon to uncover the un- 
known, or as by Galileo to confirm the known, but as a means of 
eliminating all but one of the mechanisms suggested by imagina- 
tion as the explanation of a particular phenomenon. And as 
Descartes correctly stated, the imagination is directed because it 
is referred to certain known principles (or constructs), and further 
because the mechanisms suggested must be susceptible in the 
first place of deductive check, since science does not admit of 
idle guessing. If Descartes had realized that even when only a 
single hypothetical mechanism seems deductively feasible it 
remains a hypothesis until confirmed by experiment, and if he 
had applied this test more meticulously, his thought would have 
been less liable to run into speculation. In any case the liberty to 
frame hypotheses (in spite of Newton's famous dictum), with the 
rigorous attention to the findings of experiment and observation 
which Descartes himself neglected in his encyclopaedic survey of 
nature, was to prove a creative factor in the accelerating progress 
of science. 

The scientific method of the seventeenth century cannot be 
traced to a single origin. It was not worked out logically by any 
one philosopher, nor was it exemplified completely in any one 
investigation. It may even be doubted whether there was any 
procedure so conscious and definite that it can be described in 
isolation from the context of ideas to which it was related. The 
attitude to nature of the seventeenth-century scientists especially 
their almost uniform tendency towards a mechanistic philosophy 
was not strictly part of their scientific method; but can this be 
discussed except in connection with the idea of nature? In large 
part the character of the method was determined by the mental 
range of the men who applied it; hence Bacon's method bore 
fewer fruits in his own hands because his conception of the facts 
of nature was still Aristotelean. The influence of Descartes, too, 
was so great because he produced a mechanistic world-system of 
infinite scope (enriched with some genuine discoveries) which was 
welcomed by his age, not because he outlined a remarkably clear 
or satisfactory way of proceeding in scientific research. Even 
Galileo's observations on method were probably less important 
than direct imitation of the kind of mathematical analysis he 
initiated in mechanics. Over the broad area of scientific activity 
the influence of content on form was more significant than the 


reverse effect. Methods changed, because different questions were 
asked, and a new view of what constitutes the most useful kind of 
scientific knowledge began to prevail. Perhaps this is most effec- 
tively revealed in the biological sciences, where the century 
witnessed a progressive change in the content of investigations 
unaccompanied by conscious discussions of the methods to be 
employed. Here there was no parallel to the criticism of the 
methods of Aristotle and the scholastics in physics, though of 
course the medieval neglect of the descriptive sciences was often 
commented on adversely. The far-reaching inter-action between 
the content and the techniques of science was also uncontrolled 
by any very explicit conceptions of method. This interaction had 
a profound effect on the quality and extent of the information 
available; but Bacon alone explicitly recognized the importance 
of accurate fact-gathering in science. It seems most natural to 
believe that in any effective step the method, the philosophy and 
the discovery itself were carried along together in the subsequent 
impact, for though there is nothing that can reasonably be called 
a specific method of science to be found in the works of Harvey, 
or Kepler, or Gilbert, these men changed the character and form 
of future studies. Who, for instance, could ignore the challenge of 
the phrase with which Gilbert opens his Preface to De Magnete: 
' Clearer proofs, in the discovery of secrets, and in the investigation 
of the hidden causes of things, being afforded by trustworthy ex- 
periments and by demonstrated arguments, than by the probable 
guesses and opinions of the ordinary professors of philosophy. . . .' 
Yet the meaning and weight of experimental testimony was still 
open to discussion a century later. A scientific approach to prob- 
lems must be the sum of its many aspects experimentation, 
mathematical analysis, quantitative accuracy, and so on varying 
according to the nature of the problem; and this the seventeenth 
century drew from many varied sources. Its implied implementa- 
tion in practice was more important than its explicit formulation, 
with the somewhat curious result that scientific method, shaping 
itself to the needs of practising scientists and vindicated rather by 
results than by preconceived logical rigour, has remained some- 
thing of an enigma to philosophers from Berkeley onwards. In the 
long run the obstinate empiricism of a Gilbert or the unpredictable 
intuition of a Faraday have successfully broken the rules of both 
inductive and mathematical logic. 


EA.CH phase of civilization tends to produce its own institutions 
of learning. In the ancient empires science was attached to 
the temples of religion; Greece saw Plato's Academy, the 
Lycaeum founded by Aristotle, and the vast library of Alexandria; 
the middle ages created the common school and the university in 
a structure of education which has not wholly vanished. Lastly, 
in the modern era, the learned society, with its international 
affiliations and specialized journals, has profoundly influenced 
the stratigraphy of research. Neither the learned society nor the 
learned journal (the terms are convenient, if pompous) was 
altogether the creation of the scientific revolution, but in both 
cases the course of events was very much determined by the 
necessities of the scientific movement, and scientific organization 
was taken as a model by those who worked in other fields of 
knowledge. From the end of the seventeenth century the majority 
of active men of science were members of some active scientific 
group; publication in one of the ever more numerous journals 
gradually became the recognized manner of announcing the 
results of investigation; and the national scientific society was 
accepted as the vehicle for the state's concern in scientific matters. 
Although the Fellowship of the Royal Society, for example, was 
much less indicative of intellectual distinction in the eighteenth 
century than it has since become, as institutions the Royal Society 
or the Academic Royale des Sciences enjoyed a prestige even 
greater than that of the universities in humane studies. Indeed, the 
evolution of modern science outside academic walls was the main 
cause of the lack of cohesion, and of the difficulty in the communi- 
cation of ideas, whose correction was one of the principal objects 
of the founders of the scientific societies. In the unity of medieval 
learning the scholar enjoyed communion with others of similar 
interest in the university of which he was almost invariably a 
member, and wherever his studies might lead him. The* sixteenth 
century saw the new phenomenon of scholars, literati and 

1 86 


scientists whose interests were no longer embraced in the work of 
the university, and who were also more uniformly distributed 
throughout a highly cultivated society. The landed gentleman, 
the country physician or clergyman, the apothecary, the soldier 
and the lawyer, played a new and important part in the advance- 
ment of knowledge or the patronage of literature. Expecially in 
northern Europe, where the universities were less numerous and 
more conservative than those of Italy and France, intellectual 
leadership passed to a class which was not merely outside the orbit 
of the university, but was apt to regard academic learning as old- 
fashioned and sterile. 

Oxford and Cambridge are our laughter, 
Their learning is but pedantry: 
These Collegiates do assure us, 
Aristotle's an ass to Epicurus. 

wrote the "wit" who composed the Ballad of Gresham College about 
iGGy. 1 From the first, the connection of the new scientific move- 
ment with practical arts rendered it in some degree independent 
of the universities. As the friends of the "new philosophy" became 
increasingly critical of Aristotle and conventional education, they 
found their opponents the more firmly entrenched behind 
academic walls; hence the innovators tended to seek a more con- 
genial intellectual environment elsewhere. 2 Scientific knowledge 
was no longer in the mid-seventeenth century limited to the 
religious and medical classes, but was widely diffused through a 
diversified and exuberant society. Many biographies relate the 
feeling of confidence, the depth of intellectual satisfaction, the 
release of a creative drive that was experienced by members 
of the new class of laymen, educated and leisured, when they 
passed from the confines of academic disputation to the methods 
of experimental science. 

Scientific discovery is (or was, until recent times) an act of the 
individual, with of course a greater or less indebtedness to his in- 
tellectual inheritance. So, equally, in the seventeenth century, was 
the adoption of the novel scientific outlook, critical of orthodoxy, 

1 Gresham College, founded in 1598 by the merchant-financier Sir Thomas 
Gresham, was the first meeting-place of the Royal Society, whence the Fellows 
were known as the "Gresham philosophers." 

2 In Europe, this was partly due to the control of education exercised by 
certain religious orders, but everywhere the university was deeply committed 
to Aristotelean thought. 


which can be seen almost as a conversion in many instances, 
as when Galileo became an adherent of the Copernican system. 
But since men naturally assemble to indulge a common taste, and 
since wits are sharpened by contact, the groups of intellectuals 
who collected in a tavern, a lecture-room, or about an enterprising 
patron tended to assume a more formal character, to look for 
recognition and privilege. The first of such groups to acquire an 
organization and a history were products of Italian humanism. 
Their interests were literary rather than scientific. About a century 
later the first national academy, the Academic Franchise founded 
by Richelieu in 1635, was also a literary institution: its main task 
was the conservation of the purity of the French language. The 
early literary societies met for discussion and criticism; their object 
was rather the extension of knowledge and the refinement of taste 
than anything resembling research or analysis, and there was 
nothing foreshadowing the modern presentation of papers. The 
first scientific societies, which also originated in Italy, followed the 
same pattern. Occasional meetings of groups of experimenters, 
like that which is supposed to have collected about William Gilbert 
at his London house, or that centred about Giovanbattista Porta 
in Naples (the so-called Accademia Secretorum Naturae) were 
hardly societies at all. 1 The first assembly emphatically of this 
character was the Accademia dei Lincei in Rome, of which Galileo 
was a member, which lasted with one break through the first 
thirty years of the seventeenth century. The Lincei 2 rose to a 
membership of thirty-two, and planned to set up branches every- 
where, equipped with printing-presses, botanic gardens and 
laboratories. The patron of the society was Duke Federigo Cesi, 
a naturalist, and much of its activity was diverted to natural 
history. One member, Francesco Stelluti, published the first 
zoological studies made with the aid of the microscope. Two of 
Galileo's early books were published by the Lincei, but the society 
did not approve his later cosmological ideas. 

The Accademia dei Lincei, like earlier literary societies, and some 
later scientific groups, did not engage in any form of corporate 
activity. The members followed their own investigations, whose 

1 Baptista Porta (d. 1615) was the author of Magia Naturalis Libri IV (1558, 
enlarged edn. 1589: Englished as Natural Magick, 1658), and a great exponent 
of esoteric experimentation. 

2 So called, because the Lynx symbolized the clear-sightedness of science. 


results they discussed at the meetings. However, the great Floren- 
tine society of the mid-seventeenth century, the Accademia del 
Cimento, followed the alternative plan, which had already been 
described by Francis Bacon in the New Atlantis. The object of 
Bacon's model organization was not merely to bring men together, 
but to set them to work in common on the tasks most important 
for science, so that it resembled a scientific institute more than a 
modern scientific society. The vast realm of natural knowledge, 
he felt, was too vast for one man to tackle single-handed, while 
concentration on a single problem or set of problems was likely 
to produce a myopic picture of single trees, not a survey of the 
forest. To the efforts of individual pioneers, as Sprat put it later 
in speaking of the Royal Society, 'we prefer the joint Force of 
many Men.' Other advantages of the Baconian plan were that, 
as it ensured that due attention was always paid to each division 
of science, so it made certain that none could be carried on in 
complete isolation from the rest; and it also provided a means by 
which, it was hoped, a quantity of necessary apparatus beyond 
the means of a private purse could be gathered together. 

In Bacon's view, the assembling of pure information, the 
preliminary to the elucidation of natural truths, was such a 
formidable task that it could only be tackled by a co-operative 
endeavour. Otherwise science was likely to be for ever deluded 
by theories enunciated on the basis of an insufficient mass of 
digested fact. 1 Later the Royal Society was for a short time to 
embark on such a project of fact-collection. The Accademia del 
Cimento, on the other hand, was not committed to this Baconian 
conception of procedure in science. It concerned itself with the 
experimental development of the scientific ideas of Galileo, and 
of his two most successful pupils, Torricelli and Viviani, while the 
nine members also pursued their own problems independently. 
One large fraction of their total activity was directed to the proof 
of the theorems on motion that Galileo had demonstrated mathe- 
matically, and another to the study of the barometric vacuum 

1 Thomas Sprat, in his History of the Royal Society (1667), echoed the then 
typical opinion that in Bacon's writings were 'everywhere scattered the best 
Arguments, that can be produced for the Defence of experimental Philosophy, 
and the best Directions, that are needful to promote it,' but he did not hesitate 
to confess that Bacon's natural histories were far from accurate, because Bacon 
seemed 'rather to take all that comes, than to choose, and to heap, rather than 
to register ' (1722 edn., pp. 35-6). 


discovered by Torricelli. Though the business of the society was 
experiment, it was not by any means empirical experimentation 
alone. Reports of its work, which spread slowly throughout 
scientific circles in Europe, did much to shape the course of 
experimental science elsewhere, and created new confidence in 
the Galilean experimental method. Part of the success of the 
Accademia del Cimento in spite of its short duration often years 
from 1657 to 1667 was due to the richness of the apparatus at its 
command, for it made use of what was really the first physical 
laboratory in Europe. 1 The academy was founded by the Grand 
Dukes Ferdinand II and Leopold of Florence, who used the 
remaining wealth of the Medicis to buy the services of the finest 
instrument-makers, to procure the most perfect lenses, and equip 
their colleagues with a most elaborate series of barometers, 
thermometers, time-measuring devices and whatever else was 
required for their work. 

The book in which this was described the Saggi di Naturali 
Experience (i667) 2 was almost the first piece of pure experimental 
reporting in the history of science. Interpretation of the results 
gained was limited strictly to the range of the evidence, and 
elaborate speculation was avoided. The experiments recorded 
are various as well as numerous. Attempts were made to verify 
Galileo's theory of projectiles, and the time-keeping properties of 
the pendulum were studied without, however, leading to its 
application to a mechanical clock, which was made by the Dutch 
physicist Christiaan Huygens. Various forms of the thermometer, 
hygrometer and barometer were tested, and the design of optical 
instruments improved. Experiments were made on the "radia- 
tion" of cold from a lump of ice; on the thermal expansion of 
many substances; on the incompressibility of water; on the force 
of gunpowder; and on capillary attraction. The researches of 
Torricelli and Pascal, showing that the observations formerly 
explained by the statement that nature abhors a vacuum should 
be attributed to atmospheric pressure, were confirmed. It was 
proved that neither combustion nor respiration were possible in 
a space exhausted of air, that magnetic attraction was transmitted 
through it but not sound, and a rather unsuccessful attempt to 
construct an air-pump was made. In this field of activity the 

1 Many of the instruments are still preserved in Florence. 

2 Translated by Richard Waller as Essayes of Natural Experiments (1684). 


Accademia was largely repeating work that had already been 
done by Robert Boyle at Oxford, and described in his Physico- 
Mechanical Treatise on the Spring of the Air (1660). 

Naturally the benefits to be derived from closer co-operation 
among those interested in the new scientific movement were not 
perceived in Italy alone. In both England and France informal 
groups had existed for many years before the Accademia del 
Cimento was founded. The generation of Frenchmen which in- 
cluded Descartes, Gassendi, Fermat, Desargues, Roberval, Pascal 
and Mersenne (c. 1630-60) was particularly active, fertile both in 
new ideas and new experiments. Paris was their centre, and there 
was a continuous tradition of scientific gatherings which was 
ultimately formalized in the Academic Royale des Sciences. One 
of the earliest groups was held together by the personality of Marin 
Mersenne, a Minim friar of the convent in the Place Royale, 
which was not only a meeting place at which important discussions 
took place, but also the centre from which Mersenne conducted 
his vast correspondence, maintaining communication between his 
colleagues even more effectively than the actual gatherings. It is 
a significant historical fact that, since the late sixteenth century, 
transport facilities and postal organizations had much improved, 
rendering possible regular and frequent exchanges of letters. 1 By 
this means news of the latest developments could be spread more 
rapidly: problems could be exposed for general consideration: and 
criticism could be provoked and collated. In the mid-seventeenth 
century a number of men occupied a prominent position, less 
on account of their own intellectual capacities, than because of 
their indefatigability as correspondents. Their function was to 
be acquainted with everyone of importance in science, to gather 
information and to re-distribute it to those of their friends who 
were likely to be interested. Of these Fabri de Peiresc at Mont- 
pellier was one, and Mersenne in Paris another. Later Henry 
Oldenburg, first Secretary of the Royal Society, carried on the 
same role, his talent as a "philosophical merchant" (as Robert 
Boyle called him) greatly strengthening the bonds between 
English and continental scientists. Even in the eighteenth century 
the private correspondence of a great public figure in science (like 
Sir Joseph Banks) was still of international importance. 

1 Tycho Brahe was one of the first scientists to leave an important mass of 
material of this kind, which has been edited byj. L. E. Dreyer. 


Jta London, ox in Firm, informal groups preceded a formal 
scientific society. These seem to have had a stronger common 
interest in the mathematical sciences than in moral and natural 
philosophy, partly because geometry and astronomy were well 
represented at Gresham College (the natural focus for scientific 
pursuits in London), partly in continuation of the Elizabethan 
tradition of developing the practical sciences (navigation, sur- 
veying, cartography, etc.).') While there was little evidence of 
English concern for the ideas of Bacon, Gilbert and Harvey until 
near the close of the first half of the seventeenth century, there 
was considerable activity in the field where science and technology 
overlap. Cornelius Drebbel, an ingenious engineer as well as an 
experimenter of some repute, was acclaimed at the court of 
James I, 1 whose successor, besides patronizing Harvey's researches 
in embryology, established an experimental workshop at Vaux- 
hall. Even the mathematician Napier of Merchistoun, inventor 
of logarithms, in a fit of Protestant fervour invented a series of 
terrible war-like devices, the plans for which he destroyed on his 
death-bed. On the whole, the more important exponents of pure 
science in England at this early period, like Thomas Harriot 
(d. 1621) and Jeremiah Horrocks (d. 1641), though by no means 
isolated, had slender contact with the great scientific movement 
on the Continent. 2 Dilettanti, philosophers and literary men (such 
as Thomas Hobbes, Sir Charles Cavendish and Sir William 
Boswell) did more to make its literature known in England. 
Indeed, the " grand tour" was a serious and necessary education, 
as may be seen in the life of Robert Boyle. 

The history of the emergence of the Royal Society from these 
groups has been told many times. It now seems probable that 
there were two at least of these, whose members became the fathers 
of real science in England; some men entered more than one 
circle, but there was far from complete unity of ideas. In the 
London of the Commonwealth and Protectorate men of antagon- 
istic religious and political persuasions could have very similar 

1 Who paid a state visit to Tycho Brahe's observatory at Hveen, and received 
the dedication of Kepler's Harmonices Mundi. 

2 Harriot was an inventive algebraist, and perhaps an independent dis- 
coverer of the usefulness of the telescope in astronomy. He was closely connected 
with the Elizabethan explorers. Horrocks, in a very short life, proved himself a 
theoretical and practical astronomer of genius. He was an early student of 
Kepler, with whom he had some correspondence. 


scientific aspirations. 1 Something, at least, of Bacon's influence 
may be detected in all; many wished to see some sort of specifically 
scientific institution established, not a few were firmly convinced 
that civilization could be powerfully advanced through scientific 
knowledge. These last were particularly evident in the group that 
Boyle called the "Invisible College" in 1646, who apparently 
devoted especial attention to agriculture, as well as to natural 
philosophy and mechanics. The leading figure in this group was 
Samuel Hartlib, a Polish refugee, a man of great learning and 
wide connections, an enthusiast for the union and defence of the 
Protestant churches. Hartlib was a great advocate of the applica- 
tion of science to technology, but no scientist himself. His hopes 
broken by the restoration of the monarchy, he appears to have 
played no part in the foundation of the Royal Society that soon 
followed. Another group included men of greater weight. As 
John Wallis, the mathematician, recollected the events of 1645: 

We did, by agreement, divers of us, meet weekly in London on a 
certain day and hour, under a certain penalty, and a weekly contribu- 
tion for the charge of experiments, ... of which number were Dr. 
John Wilkins . . . Dr. Jonathan Goddard, Dr. George Ent, Dr. 
Glisson, Dr. Merrett (Drs. in Physick), Mr. Samuel Foster . . . Mr. 
Theodore Haak . . . (who I think first suggested these meetings) 
and many others. 

Haak was another German refugee, probably the most im- 
portant of Mersenne's English correspondents. All those named 
by Wallis (including himself), except Foster who died in 1652, 
were Original Fellows of the Royal Society. The group met in 
term-time at Gresham College, and Wallis's list of topics in the 
"New or Experimental Philosophy" which came up for discussion 
recalls the subjects treated by the Accademia del Cimento: 

Some were then but New Discoveries, and others not so generally 
known and embraced as now they are, with others appertaining to 

1 Thus, a circle close to the government included the poet Milton, Olden- 
burg, probably John Pell (mathematician), Lady Ranelagh (Boyle's sister). 
In touch with this was another group (Boyle's "Invisible College"?), which 
included Hartlib, Boyle, Drury, Oldenburg, Plattes, Dymock, Petty, and 
evidently others. Then Wallis's group at Gresham College, also deeply com- 
mitted to the republican regime, was linked with the universities and the 
"Invisible College." Finally, the Royalists (Evelyn, Brouncker, Moray) seem 
to have maintained amicable relations with individuals (at least) in these 



what hath been called the New Philosophy which from the times of 
Galileo at Florence, and Sir Francis Bacon in England, hath been 
much cultivated in Italy, France, Germany and other parts abroad, 
as well as with us in England. 

It is interesting to note that the Copernican hypothesis was still 
debated by these philosophers. About the year 1649 they were 
divided, some moving to Oxford, where they formed the Oxford 
Philosophical Society, which was joined by Boyle on his removal 
there in 1653. In Oxford they were reinforced by some brilliant 
students, among them Christopher Wren and Robert Hooke. 
Thus there is considerable evidence that before the restoration 
there existed an extensive ramification of personal connection 
among at least thirty men, many of whom were prominent in 
academic and public life, and that their common interest was in 
mathematics and science, not in the promotion of a religio-political 
movement. The arch-royalist Evelyn could even visit Wilkins, 
Cromwell's brother-in-law. Few were too deeply committed to the 
republic to adjust themselves to the restoration of the monarchy, 
which provided an opportunity for effecting the formal organiza- 
tion long discussed among these amateurs. 1 Charles IPs dilettante 
interest in science was well known, and his scientifically minded 
courtiers, Sir Robert Moray 2 and Viscount Brouncker (later first 
President of the Royal Society), were able to win his patronage. 

The Royal Society of London for the promotion of Natural Knowledge, 
which received its first charter in 1662, was a wholly private 
creation, very different from other major societies of the century. 
Royalty gave patronage, but nothing more. The Fellows enjoyed 
neither privilege nor pension. They were granted no buildings or 
funds. Therefore the Society remained, to the nineteenth century, 
impoverished and inadequately housed. It has never possessed 

1 In addition to the proposals of Bacon, Comenius and Hartlib, plans were 
made by Evelyn, Petty and Cowley. In the latter's plan sixteen resident pro- 
fessors were to teach * all sorts of Natural, Experimental Philosophy, to consist 
of the mathematics, mechanics, medicine, anatomy, chemistry, history of 
animals, plants, minerals, elements, etc.; Agriculture, Art Military, Navigation, 
Gardening. The mysteries of all trades, and improvement of them; the Facture 
of all merchandises, all natural magic, or Divination; and briefly all things 
contained in the catalogues of natural histories annexed to my Lord Bacon's 
Organon.* (A proposition for the Advancement of Experimental Philosophy, in Cowley's 
Works, 1 680, pp. 43-5 1 ) . 

8 Moray was a close friend of Huygens, and like Oldenburg he had attended 
sessions of the Montmor academy in Paris. 


laboratories, or other than honorary means of promoting research, 
and was never able to implement the Baconian conception to 
which many of the Founders were attached. For over a century 
and a half the qualifications for a Fellowship included wealth and 
influence as well as scientific merit, because without such support 
the Society would have collapsed. On the other hand, it had a 
corresponding sovereignty over its actions. It was independent of 
government, and though the specialist knowledge of the Fellows 
was often placed at the service of the state (especially in the 
eighteenth century), state officials guided neither its elections nor 
its business. By contrast, in France the Academic Royale des 
Sciences was the creation of the first minister, Colbert, who 
arranged the appointments and suggested problems in accordance 
with political interests. The members were pensionaries when 
occasion demanded, they became civil servants. That the Dutch 
physicist Huygens, who retained his Fellowship of the Royal 
Society throughout the Anglo-Dutch wars, found his position in 
the Academic des Sciences inconsistent with Louis XIV's anti- 
Dutch policy, and resigned from it, sufficiently indicates the 
difference in character between the two institutions. And these in 
turn correspond to the different social and constitutional structures 
of the two states. 

The middle-class intellectuals, who in England combined to 
form their own clubs in which they met as equals, were in France, 
as in Italy, more dependent on the good offices of a patron. Thus, 
at the beginning of the seventeenth century, one of the groups 
most notable in Paris for literature and learning met regularly 
at the residence of the historian de Thou. His patronage, which 
included the use of his valuable library, was continued by his 
relatives the brothers Dupuy to about 1662. Less exalted gather- 
ings met at the Bureau d'Adresse managed by the journalist 
Renaudot. At these, as at the Cabinet of the Dupuys, literary and 
political news was more eagerly awaited than discussion of 
scientific topics. Mersenne's circle, however, confined its attention 
almost entirely to mathematical and scientific affairs: it was he, 
for example, who made the discoveries of Galileo and his pupils 
known in France, who gave currency to the Cartesian system, and 
publicized Pascal's problem on the cycloid. 1 After Richelieu's 

1 i.e. the calculation of the area bounded by the curve and a straight line, 
which proved to be three times the area of the generating circle. 


foundation of the Academic Frangaise there was some feeling among 
those who cultivated the sciences that encouragement ought to be 
given to a similar non-literary institution. Among their number 
was Habert de Montmor, a man of great wealth who had offered 
his patronage to both Descartes (who declined it) and Gassendi. 
Not long after the death of Mersenne in 1648 weekly meetings 
were taking place in his house, presided over by Gassendi. Their 
discussions were not limited to science, and it was required only 
that those who took part should be c curious about natural things, 
medicine, mathematics, the liberal arts, and mechanics.' The 
Montmor Academy, which gave itself a formal constitution in 
1657, soon became a fashionable resort; at the meeting in 1658 
when Huygens' paper announcing his discovery of Saturn's ring 
was read, there were present 'two Cordon Bleus . . . both Secre- 
taries of State, several Abbes of the nobility, several Maitres des 
Requetes, Conseilleurs du Parlement, Officers of the Chambre 
des Gomptes, Doctors of the Sorbonne,' after which the amateurs, 
mathematicians and men of letters seem rather insignificant. 1 
Science, even the most abstruse mathematics, had become respect- 
able, and apparently interesting, even in the upper levels of 
Parisian society. The new philosophies of Descartes and Gassendi 
were victoriously allied against Aristoteleanism. But the course of 
the Academy was not altogether smooth; the amateurs were 
more ready to discuss the latest marvels in science than to work 
for its advancement, and there were sharp clashes of personality. 

Mazarin, who had shown far less concern for the intellectual 
eminence of France than his master Richelieu, died in 1661 and 
the supreme power was then committed to the young King, 
Louis XIV. There was thus the possibility of acquiring for science 
the greatest of all patrons. Since the Royal Society had begun to 
take shape in 1660 the Montmor Academy had followed its 
fortunes with some envy, and had even to some extent modelled 
its own proceedings upon the Royal Society's example. The links 
between the two bodies were close, for Oldenburg corresponded 
with several members of the Montmor Academy. Huygens and 
Sorbire (the Secretary of the Academy) were members of both 
societies, and a number of the Parisians visited London. 

The works of Boyle and other Englishmen were carefully 

1 Saturn's ring had been seen in very distorted form by other astronomers, 
but Huygens first interpreted its nature correctly. 


studied in Paris, where the usefulness of the empirical attitude was 
gradually more highly esteemed. While the Royal Society had 
grown from its own independent and varied origins, the Academic 
des Sciences was certainly inspired by its success. In 1663 Sorbiere 
sent to Colbert, who was virtually Louis' Minister for Internal 
Affairs, a copy of his memoir on a proposed reform of the Montmor 
Academy. He regarded an experimental organization without 
royal support as hopeless; soon afterwards the Academy did indeed 
cease to exist, partly as a result of tension between the experi- 
mentalists and the philosophers. Meetings continued, however, 
at the house of Melchisedec Thevenot, 1 who also found the 
expense of providing for experiments too great, and appealed to 
Colbert. In a situation where co-operation between the Cartesians, 
the Gassendists, the amateurs, the mathematicians and the experi- 
mentalists in a joint undertaking seemed increasingly impossible, 
the latter group turned to the monarchy. Their first scheme, 
planned in an ample Baconian fashion, was severely pruned by 
the minister. Ultimately the Academic des Sciences consisted of 
two classes only, mathematicians (including astronomers and 
physicists) and natural philosophers (including chemists, physi- 
cians, anatomists, etc.), meeting jointly on Wednesdays and 
Saturdays in two rooms assigned to their use in the Royal Library. 
Appointments of the academicians were made during 1666, and 
sessions began at the end of that year. 

Most of the active members in the English groups preceding the 
Royal Society became Fellows, 2 but few of those associated with 
earlier Parisian assemblies were received into the new Academic. 
The systematic Cartesians were carefully excluded; on the other 
hand, three foreigners, Huygens, Cassini and Roemer, were 
among the most distinguished of Colbert's appointments. Thus 
the Academic des Sciences was not strictly a continuation of any 
previous body, nor did it include the amateurs and dilettanti 
admitted by the Royal Society. No rules or constitution exist 
earlier than the reorganization effected by the Crown in 1699, 
but it is evident that as in England the precepts of Bacon were not 
without weight. Huygens, especially, advocated the preparation 

1 (1620-92), traveller, linguist, author, student of many sciences, and 
inventor of the familiar spirit-level. 

2 The few who did not seem to have retired into obscurity for political or 
religious reasons, as Milton did; the election of John Ray (1667) shows that the 
Royal Society exercised considerable latitude in these respects. 


of a complete Natural History, and the examination of new 
inventions was an important aspect of the Academic's work. 
Having sketched a common programme, the pensionaries pro- 
ceeded to their experiments and discussions in concert. These 
proceedings were strictly secret. As in London, the private 
researches of the academicians gradually assumed a greater 
significance than their co-operative undertakings. Yet the 
Academic, thanks to its greater wealth, was able to attempt 
ventures beyond the resources of the Royal Society. Two of them, 
the measure of a degree of a great circle about the earth, giving 
an accurate estimate of its diameter for the first time, and the 
expedition to Tycho Brahe's observatory at Uraniborg, were 
conducted by the astronomer Picard. A third, the expedition to 
Cayenne (in which it was discovered that the length of the 
pendulum beating seconds was less in southern than in northern 
latitudes) had as its object the measurement of the earth's 
distance from the sun by means of simultaneous observations on 
Mars. 1 

Indeed, the study of astronomy by the members of the Acade- 
mic was particularly successful. They developed the telescope of 
very long focal length to its useful limit, the application of the 
telescope to measuring instruments, and the use of the telescope 
micrometer. Cassini's observations on Saturn, and Roemer's on 
Jupiter (from which he correctly deduced the finite velocity of 
light) won great fame. Some of these observations made at the 
Paris Observatory provided important evidence for the system of 
the universe which Newton was to substitute for that of Descartes. 
They were made possible by royal generosity in equipping the 
Observatory, built in 1666, which became an experimental insti- 
tution as well as an astronomical observatory in the modern sense, 
fitted with the finest instruments. For astronomy was the first of 
the sciences to reach the stage where the results obtained bear a 
definite ratio to the expenditure permitted. The Royal Society, by 
contrast, was far less well provided for. It was not placed in control 
of the Royal Observatory at Greenwich (founded in 1675), though 
it was granted some vague surveillance over it. 2 The equipment at 
Greenwich, provided in the first instance by John Flamsteed, the 

1 The result obtained was about 6 per cent, too small. 

2 This somewhat anomalous situation provoked a serious conflict between 
Flamsteed and the Society early in the eighteenth century. 


Astronomer Royal, and his friends, was limited though good of its 
kind. He himself was forced to take a country living for support, 
and could never afford proper assistance. His main work in de- 
termining the positions of the stars was not available for more than 
thirty years, but he supplied observations on the moon used by 
Newton in his gravitational theory. The credit for Flamsteed's 
great achievement in reducing the errors of astronomical measure- 
ment to a new low order, despite all the obstacles he had to over- 
come, clearly attaches to himself alone. The Royal Society had 
other observers of note, such as Robert Hooke and Edmond Halley 
(Flamsteed's successor at Greenwich), but these had to do what 
they could with their own resources. In fact the Society could offer, 
at this period, no fit facilities for scientific work of any kind, apart 
from its library and museum. 

Everywhere in Europe the formation of scientific societies illus- 
trates a dual tendency, on the one hand towards the crystallization 
of a specifically scientific organization out of informal groups 
having broader and more superficial intellectual interests, and on 
the other towards the preponderance of the experimentalists within 
the organization. In Italy, France and England there was a transi- 
tion from the discussion of natural-philosophic systems or hypo- 
theses to the verification and accumulation of fact; as the course 
of the scientific revolution laid more emphasis on deeds than on 
words, on the laboratory rather than the study, and as the prepara- 
tion of commentaries and criticisms of ancient texts gave place to 
the writing of memoirs describing the results of systematic investi- 
gation, so the characteristics of scientific organization changed 
accordingly. In the first half of the seventeenth century the func- 
tion of a scientific assembly had been to promote discussion and 
dissemination of the new idea of science, and to provide a forum 
in which, not merely before an audience of enthusiasts, but before 
the broadest cross-section of educated and literate society, the 
original thought of a Galileo or a Descartes could challenge con- 
ventional opinions in science. Patrons like the Medici brothers, or 
a newsgatherer like Mersenne, amassed the accumulative weight 
of innovation against the science of colleges and text-books. They 
presented the total case for the "new philosophy," in an intel- 
lectual environment whose dogmatic traditions were already 
disintegrating, to a new learned class freed from the sterner disci- 
pline of the old professional scholar, ready to admire acuity of 


wit, subtlety of reasoning and fertility of imagination more than 
allegiance to orthodox "sound" views. If the "new philosophy" 
was obstructed in the university, there was appeal through the 
scientific assembly to the more tolerant, eager and wealthy in- 
tellectual circles of court and capital. But the alliance between 
modern science in its early stages and the whole turbulent current 
of cultural development in the seventeenth century was inevitably 
incomplete and of short duration. Important, creative scientific 
work rapidly outdistanced the dilettante and virtuoso: rarely, for 
example, does the name of John Evelyn occur in the proceedings 
of the Royal Society printed by Birch in his History. A man of 
general culture could not see the point of detailed scientific labours, 
for whereas he might enjoy a debate on Descartes' concept of the 
animal as machine, he tended to find the naturalist grubbing in 
ditches for insects' eggs merely comic. The exploitation of the 
shift of intellectual perspectives, so fascinating in general outline, 
inevitably sank to tedium and pedantry in the eyes of those who 
sought entertainment and striking novelty. As a result, the Mont- 
mor Academy broke up, and the Royal Society failed in wide 
appeal after its first fifteen years. 

Consequently, in the second half of the seventeenth century the 
role of the scientific society changed considerably. Having become 
a thoroughly professional body, it served as a focus for the discus- 
sion of works rather than ideas. Its aim was to develop the sciences, 
rather than promote a "new philosophy." Opposition from Aris- 
totelean university teachers, or the medical profession, was hardly 
serious any longer. The scientific movement required countenance 
less than means buildings, apparatus, money for the maintenance 
of research, and methods for exchanging its results. It was found, 
for instance, that as scientific books became more truly technical, 
more fully devoted to describing research (rather than useful text- 
books or practical manuals), the publishing trade refused to handle 
them unless large sums were laid down. Or again, while there was 
an expanding commercial market for ordinary watches and clocks, 
navigational instruments, and even telescopes and microscopes, 
financial encouragement alone would induce craftsmen to hazard 
their profits in efforts to improve instruments for the advancement 
of science. In short, the task before a scientific society .was less to 
secure the scientific revolution, than to maintain its momentum 
and to reap its harvest. The founders of the Academic des 


Sciences were perhaps the first to appeal to national interest in 
this connection. 1 Earlier exponents of the utility of scientific dis- 
covery had rather looked to the improvement of the condition of 
mankind to a shift in the precarious balance between human 
powers and the forces of nature. As Bacon had put it, the ambition 
to exalt one's state was a degree less noble than the ambition of the 
natural philosopher to elevate mankind. But in the proposals put 
forward by Leibniz, for example, to establish a scientific academy 
in Germany, there seems to be a clearer statement of the case for 
investment in science as a national benefit. There the first scientific 
academy, founded at Berlin in 1700, did not develop from the 
efforts of earlier groups of amateurs. 2 The capital of Brandenburg- 
Prussia was indeed far removed from the main centres of culture 
in Germany, its university not being founded until more than 
a century later, but Leibniz had in the Elector (later King) 
Frederick I a patron willing to realize his long-matured plans. These 
had always aimed at furthering the interests of the German nation 
and raising its technological standards through the encourage- 
ment of the vernacular language and the reform of education in a 
practical direction. To attain these objects a national academy 
which should concern itself with practical applications as well as 
with the pure sciences was the first necessity. In Leibniz' view 
Germany had once enjoyed pre-eminence in useful arts, especially 
in mining and chemistry, 3 but also in horology, hydraulic engin- 
eering, goldsmith's work, turnery, forging etc. Astronomy was 
restored by the Germans, and the " Nieder-Deutschen " (Nether- 
landers) had invented the telescope and mastered navigation. 
The only remedy for the subsequent deterioration was the generous 
encouragement of science, which Leibniz coupled with the en- 
forcement of a strictly mercantilist economic policy, by which the 

1 'Sans exclure de son programme cT6tudes les sciences pures et specu- 
latives, Colbert essaie de Porienter vers les sciences appliquees a Pindustrie et 
aux arts." P. Boissonade: Colbert (Paris, 1932), p. 28. 

2 There were already active scientific groups in Germany in the late 
seventeenth century such as the Collegium Nature Curiosorum, founded by 
Lorentz Bausch in 1652 and dealing with the medical sciences, and the 
Collegium Curiosum sive Experimental , founded by Christopher Sturm of the 
University of Altdorf in 1672 and dealing with physical sciences. Neither was 
a national academy of science in any sense. 

3 'Denn weil keine Nation der Teutschen in Bergwergssachen gleichen 
Konnen, is auch Kein Wunder, dass Teutschland die Mutter der Chimie 
gewesen.' L. A. Foucher de Careil: CEuvres de Leibnitz (Paris, 1859-75), 
vol. VII, pp. 64-74. 


state should become self-sufficient. 1 As he put it in a letter to 
Prince Eugene, discussing the proposed scientific academy in Vienna: 
Pour perfectionner les arts, les manufactures, Tagriculture, les deux 
esp&ces d'architecture [i.e. civil and military], les descriptions choro- 
graphiques des pays, le travail de mini^res, item pour employer les 
pauvres au travail, pour encourager les inventeurs et les entre- 
preneurs, enfin pour tout ce qui entre dans f&conomique ou mecanique de 
Vetat civil et militaire, il faudrait des observatoires, laboratoires, jardins 
de simples, menageries d'animaux, cabinets de raretez naturelles et 
artificielles, une histoire physico-m6dicinale dc toutes les annees sur 
des relations et observations que tous medecins salaries seraient 
obligez de fournir. 2 

Leibniz, historian, mathematician, philosopher, diplomatist and 
confidential adviser of princes, in his dual devotion to science and 
Germany saw the scientific academy as a necessary instrument of 
the modern state, through which science could be made to play 
its due part in social and economic policy. He had little patience 
with those who ' considerent les sciences non pas comme une 
chose tres importante pour le bien des hommes, mais comme un 
amusement ou jeu,' and criticized the Academic des Sciences 
for this reason. 3 Science as a factor in creating national prestige, 
its role in war and in the commercial rivalry of states, were 
appreciated in England and France as well as in Germany; but 
no one who could claim high rank as a philosopher and scientist 
announced the importance of scientific organization to jealous 
statesmen more clearly than Leibniz. 

Thus, one alleviation of the obstructions to scientific progress 
was sought through the conversion of Bacon's appeal to the inter- 
ests of humanity into an appeal to the interests of the state. 4 One 

1 On mercantilism, cf. E. Hecksher: Mercantilism (London, 1935). The 
Berlin Academy was intimately linked with Leibniz* typically mercantilist 
project for the establishment of a silk industry in Brandenburg. (Foucher de 
Careil, loc. cit., pp. 280 et seq.) 

2 Ibid., p. 317, italics inserted. 

3 Letter to Tschirnhaus, January 1694 (G. I. Gerhardt, Mathematische 
Schriften, in Gesammelte Werke hrsg. von G. H. Pertz, vol. IV, p. 519). 

4 In the later seventeenth century gunpowder was still quoted as one of the 
great discoveries of the modern age. War was accepted by scientists, as by all 
men, as an inevitable human evil, and the development of the war-like potential 
of the state did not provoke moral condemnation, perhaps because this genera- 
tion experienced warfare which was more technically efficient than that of 
previous generations, but which the lessening of religious fanaticism had 
rendered less horribly destructive. Many scientists, however, commented that 
it was more noble to advance the arts of life than those of death. 


other must be briefly treated. The Royal Society approved a step 
which was calculated to increase its support in a rather different 
way, by the publication of its Philosophical Transactions, begun in 
1665. Partly a profit-seeking venture on the part of the Secretary- 
editor, Henry Oldenburg, the Transactions were also intended to 
attract the "curiosi" and "virtuosi" to the work of the Royal 
Society, and to stimulate the submission of original reports. The 
publication consisted of discourses read by Fellows at meetings 
of the Society, of letters on scientific subjects (translated, if neces- 
sary, and printed more or less verbatim), both from Britain and 
abroad, most of which also had been read at meetings, and of 
book-reviews. The modern scientific " paper," of which the first 
examples appear in the Philosophical Transactions, has in fact a 
double origin. One of its ancestors exists in the interchange of 
scientific correspondence discussing original work, which may be 
traced back to the late sixteenth century. Very many of Olden- 
burg's articles were letters with hardly more than the "Dear Sir" 
and "your obedient servant" deleted: but they were letters in- 
tended for publication. The other ancestor was the formal essay 
or discourse read to scientific groups from the early seventeenth 
century onwards. At the time, this form of presentation required 
the development of a new art of composition, for no suitable liter- 
ary or academic models existed and its perfection, leading to the 
complex machinery for scientific reporting existing today, is an 
event of historical importance. At the end of the century, however, 
the learned journal was still far from being the accepted means 
for the announcing of discoveries. Huygens, for instance, though 
he stated his results in bald (or even enciphered) language to 
the societies of London and Paris, published them completely 
only in full treatises which sometimes appeared many years 

Nevertheless, the Philosophical Transactions was immensely suc- 
cessful. Latin translations were produced at Amsterdam, and 
the Academic des Sciences prepared its own French version. 
Though Antoni van Leeuwenhoek, the great microscopist, never 
visited London and knew no language other than his native Dutch, 
he sent the accounts of his astonishing discoveries for publication 
in English in the Transactions. Oldenburg had created a new field 
of literature, which was rapidly extended; for if the Transactions 
was not the first journal to appear in regular numbers, it was the 


first to print original communications. Its predecessor by two 
months, the Journal des Sfavans, surveyed the whole field of 
learning, devoted much space to summaries of books, and merely 
reported the business of the scientific societies. The series of 
original Mgmoires of the Academic des Sciences was begun only 
after the reorganization of 1699. Many other reviews, of which 
the most famous was Bayle's Nouvelles de la republique des lettres 
(1684) followed the broad pattern of the Journal] a few others (the 
Miscellanea published by the Collegium nature curiosorum from 1670, 
and the Ada Eruditorum founded by Leibniz in 1682, the former 
restricted to the medical sciences and the latter embracing many 
aspects of learning) printed communications, but none was so 
purely descriptive in its content as the Philosophical Transactions. 
While the reviews enjoyed a steady repute among intelligent 
readers, and gave a superficial picture of the total scientific 
activity in Europe, private communication in correspondence, 
and the frequent exchange of their respective publications, was 
for the leading figures far more important. 

From the preceding account, it will be clear that during the 
mid-seventeenth century there was a tendency for all effective 
scientific activity to be focused upon some society or group. In 
the small area of England a single organization embraced every- 
one, but in France and Germany, both before and after the 
foundation of national academies, less magnificent societies 
flourished, as they did also in the Italian and other small states. 
Each of these had its own character and major preoccupations. 
Naturally also each proclaimed, with varying degrees of emphasis, 
the principal tenets of the scientific revolution. Strategic concepts, 
like that of natural law, gradually gained a universal validity; the 
practical benefits to be expected from the cultivation of natural 
science were canvassed in all parts of Europe; Aristotelean 
philosophy was everywhere condemned, and the virtues of 
mathematical analysis everywhere exalted; nearly all the societies 
embarked on elaborate programmes of experiments. The societies 
differed in character, and individual members of the same society 
differed in their opinions; in France Descartes, and in England 
Bacon, were regarded as peculiarly magisterial figures, but it is 
commonplace to find members of different societies working on 
the same or allied problems in similar ways, or to discover the 


reaction of some discussion in Gresham College upon the work of 
the Parisian academy, and vice versa. Only to a strictly limited 
degree did local or personal traditions bar the complete amalga- 
mation of the new scientific spirit. 

Perhaps this may best be illustrated in the development of a 
mechanistic view of nature during the seventeenth century. This 
proceeded at three different levels. In the first place, a mechanistic 
theory of the universe was fully described by Descartes in 1644 
(in the Principles of Philosophy] , to be supplanted by the far more 
perfect theory of Newton's Principia (iGSy). 1 Spheres and intelli- 
gences were finally banished, and the secrets of the heavenly 
motions were traced to the properties of matter and the rule of 
laws of nature. Secondly, in biology, the theory of the organism 
as a machine was taken up by the Cartesian school, and exercised 
a wide influence; this theory, of course, was the product of a shift 
in philosophical outlook. Newtonian mechanism could be shown 
to satisfy all the minutiae of evidence; biological mechanism was 
a profound hypothesis, but no demonstration of it in physiological 
terms as yet existed, or was possible. In the third place, mechanistic 
views in relation to physics and chemistry fall into an intermediate 
category. They could not be demonstrated completely, but they 
could be applied successfully in a number of particular instances. 
They were certainly philosophical in origin, and not deductions 
from definable experimental investigations, but they were 
applicable in a wide area of experimental research. 

At each of these levels, the attitude of the mechanistic scientist 
to the complexity of nature enabled him to cope with different 
fundamental problems. Pure and celestial mechanics, the most 
highly mathematical branches of science, treated of the nature 
offerees and motion. Mechanistic biology gave a new interpreta- 
tion of the nature of life, of growth and of sensation. In relation to 
physics and chemistry, the problem to which the scientist sought 
an answer was the nature and constitution of matter, in so far as 
these sciences dealt with the properties, changes and transforma- 
tions of inorganic substance. The distinctions between the three 
states of matter; differences in density and mass, hardness and 

1 The Principia exposes, of course, no mechanistic theory of the nature or 
cause of gravitational forces. Newton's conjectures, on various occasions, make 
it plain that he leaned strongly towards some form of mechanistic interpreta- 
tion. See below, pp. 272-3. 


brittleness; the nature of magnetism, electricity, gravity and heat; 
hypotheses of light and colour, all seemed to require interpretation 
in the light of some general theory of what matter is, which would 
account for the variations in observed properties between different 
kinds of material substance. Similarly the philosophical chemist, 
studying solution, volatilization, fusion, and the analysis and 
synthesis of substances effecting striking qualitative changes in 
macroscopic properties, necessarily tried to form some picture of 
what was happening to the very nature of the materials in his 
vessels. Starting from the axiom that matter is neither created nor 
destroyed, what internal modification was implied by a change 
in observable qualities? 

During the sixteenth and seventeenth centuries there was, as 
might be expected, a sharp reaction against the answers which 
Aristotle had furnished to this type of question. In the period of 
the foundation of the Royal Society and the Academic des 
Sciences various versions of a mechanistic, particulate theory of 
matter were widely entertained. As in other matters, there was a 
tendency for the scientific revolution to revert to a Greek view of 
nature older than Aristotle's. Medieval philosophers had, very 
largely, respected Aristotle's condemnation of atomistic doctrines, 
but the scholars of the renaissance and the scientists of the seven- 
teenth century, with the full text of Lucretius' exposition of Greek 
atomism in their hands, 1 preferred its use of the concepts of 
structure and physical texture in matter to Aristotle's theory of 
forms and qualities. The Greek atomists had explained the com- 
plexities of substances without making any assumptions of a 
non-material nature; indeed, if Lucretius was right in his declara- 
tion that the only realities are atoms and the vacuum in which 
they move, qualities were mere illusion, the perceptual registration 
of physical reality. 2 This was a virtue of the "mechanical" or 
"corpuscular" philosophy particularly attractive to Galileo, for 
example, who sought to penetrate by means of the process of 

1 There were about thirty editions of De Natura Rerwn (editio princeps, Brescia, 
1473) before 1600. There was a French translation in 1677, and an English 
in 1683. 

2 By contrast, in the older philosophy, forms and qualities were real, existing 
entities. If it was said that snow had the "form of whiteness," this did not 
describe the snow, but explained its optical properties. Similarly for the 
alchemists the "form of gold" was something that could be separated from the 
"substance" of gold and transferred to the "substance" of another metal, 
e.g. lead deprived of its own distinctive "form." 


abstraction from the evidence of sensation to the basic reality of 

Before Descartes' influence became significant a number of 
writers had expounded or commented on ancient particulate 
theories, drawing on the texts of Democritus, Epicurus, Lucretius 
and Hero of Alexandria. The earlier ones treated the atomistic 
doctrine purely as a theory of matter, which they freely combined 
with Aristotelean physics. Pierre Gassendi, from about 1625, was 
the first writer to attempt to develop a completely mechanistic 
physics founded on Epicurus and rejecting Aristotle, but his 
success was hardly greater than that of Lucretius, whom, except 
in matters touching on religion, Gassendi very closely followed. 
Physical properties were simply traced to the imagined size and 
shape of the component particles. In Galileo and Bacon, on the 
other hand (as already mentioned), are found the beginnings of 
a true kinetic theory, especially in relation to heat. As Isaac 
Beeckman stated it, c all properties arise from [the] motion, 
shape, and size [of the fundamental particles], so that each of 
these three things must be considered.' 1 For both Bacon and 
Galileo an important aspect of the "new philosophy" was its 
endeavour to establish, through experimental study, a theory of 
particulate mechanisms to replace the doctrines of forms and 
qualities, yet neither of them were atomists in a narrow sense. 
Bacon, indeed, wrote that the proper method for the discovery of 
c the form or true difference of a given nature, or the nature to 
which nature is owing, or source from which it emanates ' would 
not lead to 'atoms, which takes for granted the vacuum, and 
immutability of matter (neither of which hypotheses is correct), 
but to the real particles such as we discover them to be.' 2 In 
short, there is ample evidence that in the early seventeenth century 
the conception of matter as consisting of particles, whose aggregate 
might be a solid, a liquid, an air or a vapour, was commonplace 
and generally acceptable and that the properties of the aggregate 
were attributed to the nature and motions of the particles. 

In considering the development, extension and diversification 
of this generalized concept in the second half of the century, three 
traditions may be distinguished. The first is that of the strict 

1 Journal tenu par Isaac Beeckman de 1604 a J ^34> e ^. Cornells de Waard (La 
Haye, 1939-45), vol. I, p. 216 (1618). 

2 Novum Organum, Bk. II, Aphorisms i, viii. 


atomists, adhering firmly to the indivisibility of the ultimate 
particle and the absolute reality of the vacuum between atoms. 
They were the followers of Gassendi. Next, Cartesian scientists 
continued the peculiar corpuscularian doctrine of Descartes, which 
admitted the infinite divisibility of matter, and denied the vacuum. 
Finally, the experimentalists refused to commit themselves to any 
precise body of philosophic preconceptions. They learnt from both 
Gassendi and Descartes : the form of their particulate theory was 
closer perhaps to that of Gassendi, but in its application to physics 
it borrowed much from Descartes' concrete imagination. This 
experimentalist tradition in corpuscularian physics grew most 
rapidly in England, and was especially fostered by the works of 
Robert Boyle. Never a dogmatic system, it was a late development 
which played an important part in the relations between the 
French and English scientific societies. It was, in fact, a major 
product of the impact of French scientific ideas upon Englishmen 
about the middle of the century an impact which conditioned 
the nature of the scientific achievement of the Hooke-Boyle- 
Newton generation. 

Starting from the assumptions that in nature there are no occult 
forces, like gravity or magnetism, and that the universe is continu- 
ously and completely filled with matter, Descartes developed in 
the Principles of Philosophy (1644) an extraordinarily elaborate 
mechanistic and corpuscularian "model" of the physical universe. 
His particles, of which there were three species, were not atoms, 
because he imagined them as divisible, though in nature not 
normally divided. The first element was a fine dust, of irregular 
particles so that it could fill completely the interstices between the 
larger particles. The second element (matiere subtile or aether) con- 
sisted of rather coarser spherical particles, apt for motion, and the 
third element of still more coarse, irregular and sluggish particles. 
These three elements corresponded roughly to the Fire, Air and 
Earth of Aristotle, and as they were composed of the same matter, 
the elements could be transformed one into another. This was 
regarded by the Cartesians as no arbitrary hypothesis, but as a 
truth (according to Rohault) 'necessarily following] from the 
Motion and Division of the Parts of Matter which Experience 
obliges us to acknowledge in the Universe. So that the Three Ele- 
ments which I have established, ought not to be looked upon as 
imaginary Things, but on the contrary, as they are very easy to 


conceive, and we see a necessity of their Existence, we cannot 
reasonably lay aside the Use of them, in explaining Effects purely 
Material. ?1 The nature of a substance was mainly determined by 
its content of third element, its properties by the second. Since 
Descartes denied that the third-element particles had intrinsic 
weight or attraction, hardness (the cohesion of these particles) was 
attributed to their remaining at rest together, fluidity to their 
relative motion; but this motion also was not intrinsic but im- 
parted by the first and second elements. Thus in solution the 
grosser particles of the solvent by their agitation dislodged those 
of the dissolved material; if however the particles of the solvent 
were too light, or the pores of the solid material too small to admit 
them, the latter would not dissolve. When the pores between the 
third-element particles were large enough to admit a large quan- 
tity of the second element, the substance was an "elastic fluid" 
(gas), whose tendency to expand was caused by the very free and 
rapid motion of the second-element particles. Flame itself con- 
sisted of matter in its most subtle form and under most violent 
agitation, and was therefore the most effective dissolvent of other 
bodies, while the sensation of heat increased with the degree of 
motion in the particles of the heated body. Rohault notes that, 
when filed, copper grows less hot than iron because, copper being 
the softer metal, its particles do not require such violent agitation 
to separate them as do those of iron. 2 The greater motion associ- 
ated with heat was also the cause of thermal expansion. Light 
was thought to be c a certain Motion of the Parts of luminous Bodies 
whereby they are capable of pushing every Way the subtil Matter 
[second element] which fills the Pores of transparent Bodies, ' and 
secondary illumination was attributed to the tendency of this 
matter to recede from the luminous body in a straight line. Trans- 
parent bodies had straight pores through which the matiere subtile 
could pass, opaque bodies blocked or twisted pores. If this exertion 
of pressure by the luminous body were confined or resisted, it 
would grow hot. Refraction and reflection of this pressure (or 

1 John Clarke (trans.) : Rohault's System of Natural Philosophy Illustrated with 
Dr. Samuel Clarke's Notes Taken mostly out of Sir Isaac Newton's Philosophy (London, 
1723), vol. I, pp. 115-17. Jacques Rohault (1620-72) was the greatest of all 
expositors of Cartesian physics; his Traitt de Physique appeared first in 1671. 
Clarke's Notes strongly oppose Newtonian corpuscularian ideas to those of 

2 Ibid., p. 156. 



rather pulse) which is Light were explained by analogy with the 
bouncing of elastic balls. 1 In dealing with magnetism Cartesians 
were careful to emphasize that 'though we may imagine that 
there are some Particular Sorts of Motion which may very well 
be explained by Attraction; yet this is only because we carelessly 
ascribe that to Attraction, which is really done by Impulse'; as 
when it is said a horse draws a cart, whereas it really pushes it by 
pressing on the collar. 2 Magnetic effects were actually caused by 
streams of screw-like particles, entering each Pole of the earth and 
passing from Pole to Pole over its surface, which passed through 
nut-like pores in lode-stone, iron and steel, and thus were capable 
of exerting pressures on these magnetic materials. 

By theorizing in this way on the different motions of the three 
species of matter the Cartesian physicists tried to account for all 
the phenomena of physics as known in the second half of the 
seventeenth century. They had some striking contemporary dis- 
coveries on their side: for instance, the discovery that the rising 
of water in pumps and analogous effects were not due to horror 
vacui or to attraction, but simply to the mechanical pressure of the 
atmosphere. They also explained gravitation mechanically as a 
result of pressure, and extended their corpuscular ideas to chemical 
reactions. The idea of particulate matter-in-motion was therefore 
the very foundation of Cartesian science, the basis of a homo- 
geneous system of explanation. The fact that (in Rohault's words) 
' the few Suppositions which I have made . . . are nothing com- 
pared with the great Number of Properties, which I am going to 
deduce from them, and which are exactly confirmed by Experi- 
ence' was a strong reason for believing 'that That which at first 
looks like a Conjecture will be received for a very certain and 
manifest Truth.' 3 As expounded by Descartes and his successors 
this "mechanical philosophy" was illustrated by many qualitative 
experiments; but these could hardly be said to prove the Cartesian 
system, which always remained, in addition, entirely non- 

Nevertheless, Cartesian science had a great influence upon the 
Fellows of the Royal Society. Just as, in the past, Aristotle's teach- 
ing was the inevitable starting-point for scientific thought, so they 

1 Clarke, op. cit., vol. I, pp. 201 et seq. 

2 Ibid., vol. II, p. 1 66. 

8 Ibid. 9 vol. I, p. 203; vol. II, p. 169. 


often found their point of departure in Descartes. For Boyle, 
indeed, 'the Atomical and Cartesian hypotheses, though they 
differed in some material points from one another, yet in opposi- 
tion to the Peripatetic and other vulgar doctrines they might be 
looked upon as one philosophy.' While older philosophers had 
given but superficial accounts of natural phenomena, relying on 
an incomprehensible theory of forms and qualities, the moderns 
agreed in explaining 'the same phenomena by little bodies 
variously figured and moved.' The differences between the 
modern schools were rather metaphysical than physical, and did 
not greatly affect the study of the world as it actually is. 1 Appar- 
ently the English experimentalists who formed the Royal Society 
already held eclectic opinions: 'they found some reason to sus- 
pect,' wrote Hooke in his Preface to Micrographia (1665), 'that 
those effects of Bodies which have been commonly attributed to 
Qualities, and those confess'd to be occult, are perform'd by the 
small machines of Nature.' Over this wide and in many ways 
strategic area of scientific thinking the English and French socie- 
ties spoke the same language and shared a common inheritance 
of ideas. The differences between Cartesians and Gassendists were 
found in both alike, and the appeal to a particulate theory of 
matter was as common in England as in France. 

Though the experimenters of Gresham College were far from 
being pure empiricists, in giving high praise to Descartes' system 
they did not forget their other allegiances to Bacon, Galileo and 
Gilbert. Few were dogmatic or literal followers of Descartes. 
Accepting the general form of the "mechanical philosophy," they 
measured Cartesian science rigorously by the experimental test. 
Hooke challenged its theory of light and colours, Boyle its theory 
of elastic fluids, and Newton its cosmology. Yet even the last of 
these suggested a space-filling aether, and questioned whether the 
most subtle effects of nature were not obtained by purely mechani- 
cal means. The very titles of Boyle's works indicate the tendency 
of his thought: The Excellence and Grounds of the Mechanical Philo- 
sophy] The Origin of Forms and Qualities, an introduction to the same; 
The Mechanical Origin of Volatility and Fixedness] The Mechanical 
Production of Electricity] The Mechanical Origin of Heat and Cold] with 
many more in a similar vein. And during the greater part of his 

1 Certain Physiological Essays (publ. 1661 but written some years earlier). 
Works, ed. T. Birch (London, 1772), vol. I, p. 355. 


scientific career, from about 1655 at least, he devoted himself to 
trying 'whether I could, by the help of the corpuscular philo- 
sophy . . . associated with chymical experiments, explicate some 
particular subjects more intelligibly, than they are wont to be 
accounted for, either by the schools or [by] the chymists.' 1 In his 
Excellence and Grounds of the Mechanical Philosophy Boyle defined his 
position exactly: 

God, indeed, gave motion to matter; ... he so guided the motions 
of the various parts of it, as to contrive them into the world he de- 
signed to compose; and established those rules of motion, and that 
order amongst things corporeal, which we call the laws of nature. 
Thus, the universe being once fram'd by God, and the laws of motion 
settled, and all upheld by his perpetual concourse, and general provi- 
dence; the [mechanical] philosophy teaches, that the phenomena of 
the world, are physically produced by the mechanical properties of 
the parts of matter, and that they operate upon one another accord- 
ing to mechanical laws. 2 

Here Boyle appeals for justification of his natural philosophy to 
the divine plan of creation (thus withdrawing himself from the 
atheistic connotations of Epicureanism, and from the evolutionary 
suggestions of Descartes) ; seeing the world as a machine indeed, 
but a machine whose complex processes are continually supervised 
by a divine providence. Though his world-picture transcended 
the evidence of experimental science, Boyle was convinced that 
the details of the mechanism of nature could only be revealed 
through experimental study. It might even be more useful not to 
attempt at this stage to relate observed physical phenomena to 
the 'primitive and catholick affections of matter, namely bulk, 
shape, and motion,' but rather to intermediate physical proper- 
ties such as hardness, temperature and so forth. Therefore he did 
not hesitate to doubt the necessity of Descartes' rectitude. He 
doubted whether the air in an exhausted vessel was really replaced 
by a matiere subtile, of whose existence he was generally sceptical. 3 
He attributed the elasticity of air to the springiness of its particles. 
He was much more vague in his pronouncements on the basic 

1 Some Specimens of an Attempt to make Chymical Experiments useful to illustrate 
the Notions of the Corpuscular Philosophy. Works, 1772, vol. I, p. 356. 

2 Peter Shaw: Works of Boyle abridged (London, 1725), vol. I, p. 187. 

3 The matiere subtile (or aether) in an exhausted space was used by Cartesians 
generally to explain the transmission of light, and by Huygens to account for 
effects of surface tension in vacuo. 


structure of matter than Descartes, indicating only that he thought 
it composed of fundamental particles, and larger aggregates of 
these, the real corpuscles. The particulate theory was related by 
Descartes to the Aristotelean four-element doctrine, but not by 
Boyle. He was sceptical also of the Cartesian interpretation of mag- 
netism and electricity. He carried through a far more thorough- 
going mechanistic attack on the doctrine of " forms" than the 
Cartesians. Moreover, while the Cartesians sought to illustrate a 
theory of nature by experiments, Boyle sought to interpret his 
experimental researches in the light of the corpuscular philosophy. 
The distinction is perhaps subtle, but it is real. For besides his 
sense of the ultimate truth of a mechanistic view of nature, Boyle 
was also imbued with Bacon's conception of the scientist's com- 
piling histories of nature, and promoting the progress of material 
civilization. In the last resort his devotion to the corpuscular 
philosophy seems to have been grounded less on an opinion that 
it was a key to the final understanding of nature, than on the con- 
viction that it provided a broad framework of ideas within which 
scientific research could most rapidly progress towards this final 

If Boyle presented the corpuscular philosophy more elaborately 
than any other Englishman, the influence of Newton on non- 
Cartesian particulate theories of matter was perhaps of even longer 
duration. His successors did not hesitate to read the Queries ap- 
pended to Newton's Opticks (1704) as though they were state- 
ments of his considered opinions. Newton's views on the structure 
of matter are indeed shadowy. The famous Hypotheses non jingo is 
not to be taken too literally, but he certainly would not have ac- 
cepted Rohault's easy dictum that a conjecture agreeing with the 
properties of things may be taken as very probable. The questions 
which Newton felt impelled to ask, and the answers to them at 
which he hinted, were indeed only made public because Newton 
knew that his scientific career was over. The experiments needed 
to gain further insight into these problems he would never per- 
form. Yet Newton had confidence enough in his opinions to 

It seems probable to me, that God in the Beginning form'd matter in 
solid, massy, hard, inpenetrable, movable Particles, of such Sizes and 
Figures, and with such other Properties, and in such proportion to 
Space, as most conduced to the End for which he form'd them. . . . 


These, then, were true atoms; endowed with 'a Vis inertia, 
accompanied with such passive Laws of Motion as naturally result 
from that Force/ and with 'certain active Principles, such as is 
that of Gravity, and that which causes Fermentation, and the 
Cohesion of Bodies.' Such principles were not occult qualities, 
like those of the Aristoteleans, because they were made precisely 
known by experiment; only the causes of them were hidden. 1 Of 
the particles Newton asked, have they not also 'certain Powers, 
Virtues, or Forces, by which they act at a distance, not only upon 
the Rays of Light for reflecting, refracting, and inflecting them, 
but also upon one another for producing a great Part of the 
Phaenomena of Nature?' 

He confessed that these " Virtues" might be veritably performed 
by impulse, but their cause was only to be unfolded through study 
of the "Laws and Properties of the Attraction." 2 To attraction 
between particles he attributed cohesion and the strength of 
macroscopic bodies, the force being very strong in immediate 
contact, but reaching ' not far from the Particles with any sensible 
Effect.' Thus the particles were compounded (as Boyle had sug- 
gested) into corpuscles of weaker attractive force, and so success- 
ively into the largest aggregates 'on which the Operations in 
Chymistry, and the Colours of Natural Bodies depend, and which 
by cohering compose Bodies of a sensible Magnitude.' 3 Newton 
was the first to point out that in any apparently solid body the 
volume of matter is small compared with the volume of space 
between the particles, and to think of each particle as surrounded 
by a field offeree. Again, he asked: 

Is not . . . Heat . . . conveyed through the vacuum by the vibra- 
tions of a much subtiler Medium than Air, which after the Air was 
drawn out remained in the Vacuum? And is not this Medium the 
same with that Medium by which Light is refracted and reflected. . . . 
And is not this Medium exceedingly more rare and subtile than the 
Air, and exceedingly more elastick and active? And doth it not 
readily pervade all Bodies? And is it not (by its elastic force) expanded 
through all the Heavens? 

But this Newtonian aether was very different from the Cartesian. 
As the cause of gravity Newton imagined it as being more rare 

1 Sir Isaac Newton: Opticks (with Introduction by Sir E. T\ Whittakcr, 
London, 1931), pp. 400-1. 

2 Ibid., pp. 375-6. 3 Ibid., pp. 389, 394. 


in solid bodies than in free space; where it must be of the order 
one million times less dense than air, but more elastic in the same 
proportion. 1 With regard to the theory of light, it seems futile to 
try to harmonize the different notions referred to in the Queries. 
Newton's views involved a compromise between the "undulatory " 
and "corpuscular" theories, and in different passages he seems, 
as it were, to be operating at different depths of thought. But 
whether he spoke of light as a vibration in the aether, or as a 
stream of particles issuing from the luminous body, he was at 
once mechanistic and anti-Cartesian. Similarly he gave a purely 
mechanical account of the physiological nature of vision. 

The Queries are highly suggestive. The reader half-glimpses 
entrancing vistas of the territory to be conquered by the " me- 
chanical philosophy." In the early eighteenth century a number 
of rather unfruitful attempts to take Newton's ideas further were 
made, especially in relation to chemistry with the notion of 
corpuscular attraction as a precursor of affinity. He has been 
regarded as one of the founders of nineteenth-century atomic 
theory, and perhaps the very fact that the mighty Newton had 
speculated in this way made atomism more respectable at a time 
when the Cartesian system of science had passed into oblivion, 
and many matter-of-fact chemists distrusted John Dalton as a 
weaver of idle fancies. Certainly the less specialized corpuscularian 
and mechanistic concepts had the best chance of survival; 
Cartesian mechanism, the dinosaur of seventeenth-century 
scientific thought, could not adapt itself to a new intellectual 
environment. It was committed dogmatically in too many points 
of detail where it proved to be false. 

Only with the passage of time, and usually in relation to points 
of precise detail, did the development of scientific activity in 
Britain after the foundation of the Royal Society begin to follow 
this definitely less specialized course, yielding a mechanistic 
philosophy that was ultimately anti-Cartesian. More than two 
decades passed, after the death of Descartes in 1651, before his 
works acquired their greatest fame and authority, and before the 
character of his system became rigid. Meanwhile, the prestige of 
Gassendi was falling in France, and that of Descartes in England 
especially through the success of new ideas concerning light 
and gravitation. The Academic des Sciences became, before the 

1 Ibid., pp. 349-52. 


end of the century, more deeply committed to Cartesian thought; 
the Royal Society more ready to criticize it. It is important to 
realize that the somewhat singular character of the Royal Society 
during its first half-century was due, not solely to the Fellows' 
greater assiduity or success in experimentation emphasis on the 
purity of their empiricism is certainly to be suspected but to 
experimentation combined with a definite eclecticism of outlook, 
within the broad framework of a mechanistic, corpuscularian 
science which was becoming almost a commonplace. The intel- 
lectual tension between the English scientific groups, on the one 
hand, and the French and German on the other, certainly in- 
creased between about 1665 and 1720, the substantial difference 
between Cartesians and non-Cartesians being exacerbated by the 
adventitious dispute between Leibniz and Newton over the inven- 
tion of the calculus, but this should not be allowed to conceal the 
fundamental similarity of their attitudes, on which Boyle had 
insisted, and of their approach to scientific research. Although the 
national organization of science facilitated a deplorable kind of 
national partisanship most vicious in the early years of the 
eighteenth century, beneath this there existed a fundamental 
community of thought and activity. Broadly, the tendencies 
of science were everywhere in the same direction, and in the 
later eighteenth century, in a different situation, the friendly co- 
operation between scientific societies was once more of the 
greatest importance. 



t 1 ^HE renaissance of science in the sixteenth century, and the 
I strategic ideas of the first phase of the scientific revolution, 
JL owed little to improvements in the actual technique of 
investigation. Before the beginning of the seventeenth century 
there is little evidence, except perhaps in anatomy and astronomy, 
of any endeavour to control more narrowly the accuracy of 
scientific statements by the use of new procedures, still less to 
extend their range with the aid of techniques unknown to the 
existing tradition of science. Even the refinement of observation, 
begun in anatomy by Vesalius and his contemporaries and in 
astronomy by Tycho Brahe, hardly involved more than the natural 
extension and scrupulous application of familiar methods. Since 
the apparatus and instruments available were crude and limited 
the means were not at hand for gaining knowledge of new classes 
of phenomena, or eliciting facts more recondite than those already 
studied. Though greater reliance was placed on observation and 
experiment, the change in the content of science could not be 
dramatic and other sources of information were, at least till the 
latter part of the sixteenth century, largely traditional. Aristotle, 
Pliny, Dioscorides, Theophrastus and Galen were still very highly 
respected. Gradually, however, the tendency to supplement this 
book-learning, checked by personal examination where possible, 
by the experience of various groups of practical men gained 
ground. The wealth of fact was augmented by admitting the 
observations of craftsmen, navigators, travellers, physicians, sur- 
geons and apothecaries as worthy of serious consideration, and thus 
the status of purely empirical truths, hardly inferior to that of the 
systematic truths of physics or medicine, was in time enhanced. 
In this respect, as in others,tfthe work of Galileo gives a useful 
indication of a turning point, displaying in various ways the opera- 
tion of the new technical, as distinct from conceptual, factors 
in the development of science. His practical, almost materialistic 



intellect, stripping from natural philosophy the vestiges of its 
metaphysical connotations, led him to admire the technological 
achievements of his time and to appreciate the scientific prob- 
lems suggested by them. By revealing the value of mathematics 
as a logical instrument in scientific reasoning, he transformed, 
if he did not actually create, an important method of inquiry. 
His exploration of the potentialities of the telescope and other 
instruments shows his concern for the enlargement of the scope of 
observation and experiment through newly invented techniques. 
It is typical of the evolution of the apparatus of science during the 
seventeenth century that Galileo's results were more notable for 
their qualitative originality than for quantitative accuracy, since 
the necessity for precision in measurement was less apparent than 
the strange novelties which the new techniques unfolded. Though 
the perspective in which science regards nature changed markedly 
in the sixteenth century, it was only in the seventeenth that a sig- 
nificant qualitative change occurred in the image itself, to which 
the technical resources used by Galileo contributed profoundly. 

It has already been pointed out that the ideal of social progress 
was also a commonplace among seventeenth-century scientists, 
and that with varying degrees of assurance the attainment of this 
ideal was linked with the application of scientific knowledge to 
technology. Conversely, it is clear that scientific research is itself 
dependent upon the level of technical skill, especially when the 
endowment or organization of science compel the experimenter 
to rely upon the skills acquired by the craftsman in the normal 
course of his trade, as was the case before the nineteenth century. 
Perhaps, in the early stages of a science, it is even more important 
that the investigator should be amply provided with both prob- 
lems and the materials for solving them by the technological 
experience to which he has access. This is partly a question of 
attitudes the ability to receive the stimulus from a merely 
practical quarter partly of the richness of the techniques. Galileo 
makes Sagredo remark, on the first page of the Discourses: 

I myself, being curious by nature, frequently visit [the Arsenal at 
Venice] for the mere pleasure of observing the work of those who, on 
account of their superiority over other artisans, we call " first rank 
men." Conference with them has often helped me in the investigation 
of certain effects including not only those which are striking, but 
also those which are recondite and almost incredible. At times also 


I have been put to confusion and driven to despair of ever explaining 
something for which I could not account, but which my senses told 
me to be true. 

It can hardly be doubted that the dialogue of the First Day in this 
work was influenced by such practical observation, and it was 
from a workman that Galileo learnt of the break-down of the 
horror vacui theory when the attempt was made to lift water through 
more than thirty feet by means of a suction pump. Bacon also 
wrote of the knowledge concealed in skilled craftsmanship. In the 
next generation Boyle thought that only an unworthy student of 
nature would scorn to learn from artisans, from whom knowledge 
could best be obtained; for 

many phenomena in trades are, also, some of the more noble and 
useful parts of natural history; for they show us nature in motion, 
and that too when turn'd out of her course by human power; which 
is the most instructive state wherein we can behold her. And, as the 
observations hereof tend, directly, to practice, so may they also afford 
much light to several theories. 1 

Such opinions did not spring from theoretical reasoning alone. 
They express the new philosophy's concern for realia, but they also 
recognize a genuine historical fact, that many of the ordinary 
operations of household and workshop were quite beyond the 
reach of scientific explanation. To remedy this, Galileo began the 
theory of structures and Boyle the study of fermentation in food- 
stuffs. Many of the problems suggested by the " naturalist's insight 
into trades" could not, of course, be very profitably handled in 
the seventeenth century and some of the most intractable like 
fermentation were in any case very old. On the other hand, the 
inquiry into geomagnetism begun in the late sixteenth century is 
an example of a branch of science originating in the recent 
observations of practical men and followed up with profit to both 
theory and practice. Time-measurement also was both a scientific 
and a commercial problem, especially in relation to navigation. 
More obviously, skill in glass- and metal-working, especially 
grinding, turning and screw-cutting, could be readily applied to 
scientific purposes. Improvements in such arts were sought 
by scientists and craftsmen together, as when Robert Hooke 
collaborated with the famous clock-maker, Thomas Tompion. 

1 Considerations touching the Usefulness of Natural Philosophy; Shaw's Abridge- 
ment, vol. I, pp. 1 29-30. 


In three related sciences, chemistry, mineralogy and metallurgy 
the pre-eminence of art over science was very marked at the 
opening of the sixteenth century. In natural philosophy there was 
a rudimentary knowledge of the classification of gems, earths and 
ores together with a wholly useless theory of the generation and 
transformation of substances. The pseudo-science, alchemy, had 
its own theory of the nature of metals and their ores, and contained 
some sound information on chemical processes and the preparation 
of simple inorganic compounds. But during the previous three 
centuries its originally useful content had become garbled and 
obscured through the growth of esoteric mysticism and the 
propagation of absurdities in its name. By contrast, great progress 
in chemical industry, at a time when this represented almost the 
only rational body of chemical knowledge, was scarcely reflected 
at all in scientific writings before the mid-sixteenth century. There 
were changes, permitting the use of new materials, economy of 
manufacture, or the improvement of the product, in a long list 
of trades, all of which depended on chemical operations, such as 
the extraction of metals and the refining of precious metals, glass- 
and pottery-making, the manufacture of soda and soap, the re- 
fining of salt and saltpetre and the manufacture of gunpowder, 
the preparation of mineral acids, and distillation. Other chemical 
arts, like dyeing and tanning, were probably less improved; some 
later innovations, like sugar refining, immediately aroused scien- 
tific interest. The knowledge of the craftsmen concerned was, of 
course, wholly empirical; they were uninterested in theory, and 
given to superstition and prejudice. Part of their skill may have 
derived from the Greek scientific tradition through Islamic 
sources the art of distillation was clearly derived in this way, 
but it was perfected by artisans, not by philosophers or alchemists. 
Much of their skill was the tardy fruit of long experience. Taken 
altogether, craft knowledge in chemistry and related sciences im- 
plied a far greater acquaintance with materials and command over 
operations than were available to the philosopher or the adept. 

By the end of the sixteenth century something like a rational 
chemistry was coming into existence, though sixty years later 
Boyle could still write: 

There are many learned men, who being acquainted with chymistry 
but by report, have from the illiterateness, the arrogance and the 
impostures of too many of those, that pretend skill in it, taken 


occasion to entertain so ill an opinion as well of the art as of those 
that profess it, that they are apt to repine when they see any person, 
capable of succeeding in the study of solid philosophy, addict himself 
to an art they judge so much below a philosopher . . . when they 
see a man, acquainted with other learning, countenance by his ex- 
ample sooty empirics and a study which they scarce think fit for any 
but such as are unfit for the rational and useful parts of physiology 
[science]. 1 

In the course of that century a number of books had appeared 
which, although primarily concerned with technological processes, 
had a significant influence on the chemical group of sciences. 
Avoiding theory, they threw off the air of mystery. They described 
in a matter-of-fact way how mineral substances were found in 
nature, extracted, and prepared, and how further commercial 
products were obtained from them by the operations of art. The 
processes described required mineralogical and chemical know- 
ledge, manipulative skill, and often a complex economic organi- 
zation. Some of the German mines already absorbed heavy 
capital expenditure, and some processes, like the manufacture of 
nitric acid needed for the separation of gold from silver, were 
conducted on a considerable scale. 

The first of these treatises was a small German work known as 
the Bergbiichlein, printed at Augsburg in I5O5. 2 Before this, in the 
fifteenth century, there had been in circulation manuscripts 
written in German dealing with pyrotechnics, the preparation of 
saltpetre and the manufacture of gunpowder, but these were never 
printed and seem to have been unimportant in science. Possibly 
there were similar "handbooks," earlier than the invention of 
printing, dealing with mining and metallurgy. The Bergbuchlein 
describes briefly the location and working of veins of ore, and is 
followed in the Probierbiichlein (first printed about 1510) by an 
account of the extraction, refining and testing of gold and silver. 
Their usefulness is proved by the many editions published. The 
same subjects were treated by Biringuccio in 1540, by Agricola in 
1556, and by other German authors later in the century. The best 
informed of these was Lazarus Ercker, superintendent of the mines 
in the Holy Roman Empire, whose Treatise on Ores and Assaying 

1 Works (cd. Birch, 1772), vol. I, p. 354. 

2 A. Sisco and C. S. Smith: Bergwerk- und Probierbiichlein (New York, 1949). 
Cf. also Anncliese Sisco in Isis, vol. 43, 1952. 


(Prague, 1574), was translated into English as late as 
Ercker's thoroughly practical book is chiefly concerned with the 
precious metals, but has chapters on working with copper and 
lead, on quicksilver, and on saltpetre. The Pirotecknia of Vanoccio 
Biringuccio and the De re Metallica of Agricola both cover a wider 
range of topics. 2 Biringuccio, for instance the only Italian author 
of an important work of this type describes the blast furnace, 
bronze- and iron-founding, and glass manufacture, but the tech- 
nical information is somewhat unspecific. Agricola's book, mas- 
sively detailed in its account of geological formations, mining 
machinery and chemical processes is justly regarded as the master- 
piece of early technological writing. Agricola [germanice Georg 
Bauer] was a scholar, corresponding with Erasmus and Melanch- 
thon, writing good Latin, enriching his observations with appro- 
priate quotations from classical authors. He wrote also On the 
Nature of Fossils and on other scientific subjects. His knowledge of 
mining and industrial chemistry was gained through long resi- 
dence, as a physician, in the mining towns of Joachimsthal in 
Bohemia and Chemnitz in Saxony. About the first third of De re 
Metallica is given to a discussion of mining methods. Then Agricola 
passes on to describe the assaying of ores to determine their 
quality, and the operations of preparing and smelting them. 
Iron, copper, tin, lead, bismuth, antimony and quicksilver are 
considered as well as the precious metals. The testing of the base 
metals for gold and silver content is the next topic, followed by 
an account of the separation of precious and base metals, and 
of gold from silver. Here the various processes of cupellation, 
cementation with saltpetre, liquation with the use of lead, amal- 
gamation with mercury, refining with stibnite, and extraction 
with what Agricola calls aqua valens are described at length. This 
last was, apparently, a mixture of mineral acids prepared by 
distillation of different mixtures of vitriols, salt, saltpetre, alum 
and urine. The last section of the work treats of the preparation 
of "solidified juices" salt, potash and soda, alum, saltpetre, 
vitriols, sulphur, bitumen and glass. Here Agricola was on less 
firm ground and was guilty of some confusion and error. 

1 Modern translation by A. Sisco and C. S. Smith (Chicago, 1951). 

a The former translated into English by M. Gnudi and C. S. Smith (New 
York, 1943); the latter by H. G. and L. H. Hoover (London, 1912; New York, 


This series of technical books reflects a tradition in applied 
science that had grown slowly in the later centuries of the middle 
ages, that was still gradually increasing in skill, and was capable 
of producing new techniques for handling the unprecedented 
richness of the South American mines. The authors, like the 
contemporary anatomists and herbalists, took full advantage of 
the art of wood-cut illustration. They did their work so well that 
it lasted into the early eighteenth century, when a new era of 
technology was beginning; it was over Agricola's great folio that 
Newton pored when he was investigating the chemistry of metals. 
Chemical industry did not merely furnish the chemists of the late 
sixteenth and seventeenth centuries with the materials in their 
laboratories; it supplied them with a factual account of the 
occurrence of minerals in the natural state and the methods of 
their preparation. More than this, the technical treatises provided, 
in contrast with the fanciful symbolic language of the alchemists, 
a precise account of basic chemical operations and reactions. 
Besides the works already mentioned, the philosophical chemist 
and virtuoso could turn to the Distillation-book of Hieronymus 
Brunschwig (1512) and its successors for instruction in this most 
necessary, and most difficult, of chemical arts. The alchemists, 
even when honest, wrote on the principle that if the reader had 
not been admitted to the secrets he would fail to understand, and 
if he had he would scarcely need further guidance. These writers, 
however, set forth the best of their knowledge as plainly as 
possible; and it was likely to be sound, for as Boyle remarked, 
' tradesmen are commonly more diligent, in their particular way, 
than any other experimenter would be whose livelihood does not 
depend on it.' Only in its practical applications, stripped to its 
bare essentials of preparing this from that, was chemistry on a 
really solid foundation, independent of the misleading implica- 
tions of false, and often fantastic, theories. But the chemical 
operations of industry were not merely qualitatively reliable and 
instructive. The application of quantitative methods to a chemical 
reaction was the essence of assaying, for example in calculating 
the quantity of gold in an alloy by carefully drying and weighing 
a precipitate. 

The assayer deserves as much credit as the observational astronomer 
for providing numerical data and establishing the tradition of accu- 
rate measurement without which modern science could not have 


arisen. Though more of a craftsman than a scientist and more con- 
cerned with utility than with intellectual beauty, the assayer never- 
theless collected a large part of the data on which chemical science 
was founded. 1 

When, in the eighteenth century, the balance was recognized as 
an invaluable tool in research the chemist was only extending 
a technique whose specialized usefulness in assaying was long 
familiar. Even the law of the conservation of mass was no more 
than a theoretical statement of a truth on which the operations 
of this craft were founded. 

Boyle once spoke of German as the "Hermetical language," 
because so many alchemists had used it. It is perhaps a more useful 
observation that rational chemistry began with accounts of the 
elaborate chemical industry in Germany, and was continued by 
German experimenters, some of them inspired by Paracelsus, 
himself a German-Swiss. Here there seems to be a clear case for 
believing that the development of a technical art to the necessary 
point in complexity and achievement provided much of the basis 
of fact and method from which experimental sciences could 
arise. Of course, the roots of modern chemistry, mineralogy and 
metallurgy are also to be found in alchemy, in pharmacy, and in 
philosophy. To the formation of chemical theories in the seven- 
teenth and eighteenth centuries the description of practical opera- 
tions contributed very little. Ideas were derived from different 
sources; and there was even a muddled, wrong-headed tradition 
of laboratory work in alchemy parallel to operations on the in- 
dustrial scale. Yet in many ways the outlook of Black or Lavoisier 
resembles that of a practical assayer more than it does the esoteric 
perspective of Raymund Lull, Paracelsus or " Basil Valentine." 
The influence of the artisan, conceived as closer to the realities 
of nature than the abstracted philosopher, was an important 
element in many of the nascent sciences, but nowhere more 
than in chemistry, which most of all required an alliance of sane 
thought and reasoned activity. 

In the seel aspect- 64Se role of technical factors in the 
scientific revolution, the technique of mathematical analysis offers 
a good example of a factor internal to science itself influencing 
the progress of certain branches, in this instance mechanics and 

1 Smith: Lazarus Broker's Treatise on Ores and Assaying (Chicago, 1951), p. xv. 


astronomy! In a similar manner chemistry was another internal 
factor affecting the progress of physiology, but this was scarcely 
realized as yet.frhe ambition to formulate theoretical propositions 
and experimental results in the form of mathematical functions, 
nourished in some men by reflections of Platonic OP Pythagorean 
philosophy, was commonly entertained in the seventeenth century, 
even by those little learned in mathematics. As Boyle foresaw, 'A 
competent knowledge in mathematics is so necessary to a philo- 
sopher that I scruple not to assert, greater things are still to be 
expected from physics, because those who pass for naturalists have 
been generally ignorant in that study.' 1 The singularly happy 
synthesis^ of mathematical reasoning and experiment in geo- 
metrical optics and mechanics was regarded as a model to be 
imitated in other parts of science, and it was recognized that a 
mathematical demonstration has a rigour, and sometimes a 
generality, not easily obtained in other arguments. The study of 
mathematics, for the sake of its beneficent effect upon the intel- 
lectual powers, as an introduction to natural and moral philo- 
sophy, and as a necessary preliminary to certain professions, was 
by degrees granted a more prominent place in education} It was 
readily seen that the practical sciences navigation, cartography, 
surveying, gunnery owed their origin to the combination of 
mathematical method with more exact instrumental measure- 
ment. They had thus gained a certainty impossible with rule-of- 
thumb procedures. (About the middle of the seventeenth century 
it was found that the vagaries of chance, in the throw of a die or 
the odds in betting, were not immune to the laws of mathematics. 
The calculus of probabilities was begun. Closely connected with 
this were the first essays in statistical analysis, by John Graunt and 
Sir William Petty in England, which proved that even the hazards 
of human life were not beyond computation. From such crude 
beginnings developed an impressive mathematical apparatus of 
immense importance to theoretical physics in the nineteenth 

These analogies, of very different kinds, suggested that where 
quantitative observation and experiment were possible, a mathe- 
matical formulation ought to be adopted. Galileo had shown the 
splendour of the prize that might be won. If the workings of nature 

1 Usefulness of Natural Philosophy; Philosophical Works, abridged by Peter Shaw, 
vol. I, p. 1 1 8. 



were regular and uniform, should not they ultimately reveal a 
mathematical harmony Jas Kepler thought? In the study of acous- 
tics, during the seventeenth century, it was indeed found that 
harmonies pleasing to the ear were produced by the vibrations of 
different strings when their lengths, thicknesses and tensions agreed 
with simple mathematical ratios. More generally, Cardano in the 
sixteenth century had reviewed the physical applications of the 
rules of proportion, while Petty examined, in a paper in the Philo- 
sophical Transactions , the special significance of the quadratic ratio 

in nature ( that is, functions of the type a = kb 2 , a = ) . Again, 

r ... 

if (the mechanical philosophy was justified in its belief that the 
physical properties of macroscopic bodies result from the shape, 
size and motion of the particles composing them, ought not all 
these properties of the particles to be susceptible of mathematical 
discussion, which was already making great progress with the 
study of motion? And, indeed, by making certain measurements 
in connection with the phenomenon of optical interference, and 
examining them mathematically, Newton was able to make 
quantitative statements about the nature of light. Furthermore, 
mathematical analyses enabled him to prove that some conse- 
quences of the Cartesian theory of matter were quite incompatible 
with observation. 

The limitations to the extension of the mathematical method, 
flourishing in dynamics, to the whole of physics and a fortiori to 
still less "exact" parts of science were obviously of two kinds. The 
first lay in the ability of physicists and others to design experi- 
ments and produce results of a form suitable for mathematical 
analysis; the experimental physicist had to discover in what ways 
mathematics could help him before he could become a mathe- 
matical physicist. This kind of limitation had vitiated all attempts 
towards a mathematical theory of projectiles before the time of 
Galileo. 1 The second limitation is in the nature of mathematics 
itself, in its ability to perform the operations required.) For ex- 
ample: Boyle's experiment on the compression of a volume of air 
in one limb of a U-tube by a column of mercury poured into the 

1 The parabolic trajectory of a projectile in a vacuum was first established 
by Bona ventura Cavalieri in Lo Specchio Ustorio (1632), six years before Galileo's 
much fuller treatise appeared. The problem was easily solved mathematically 
with the aid of Galileo's theorem on acceleration. 


other (described in A Defence of the Doctrine touching the Spring and 
Weight of the Air, 1661) gave quantitative results which could be 
simply interpreted to yield "Boyle's Law" (pv = k). It was also 
found that the height of the mercury column in a barometer falls 
as the instrument is carried progressively higher above sea-level, 
because the weight of the atmosphere above decreases. The cele- 
brated experiment was carried out by Perier, on the suggestion of 
Pascal, in I648. 1 From a combination of these facts, it was realized 
that it should be possible to frame a mathematical theory which 
would enable the vertical distance between two stations, to be 
calculated from the difference in atmospheric pressure found from 
simultaneous readings of two barometers. To make a rough ap- 
proximation is sufficiently easy, but an accurate calculation 
involved purely mathematical difficulties which were not fully 
overcome in the seventeenth century. 

Discussion of the first group of these factors limitinguhe applica- 
tion of the mathematical method to science must, naturally, 
belong to the history of the separate branches of science. It would 
be necessary to discuss, in each case, the steps by which experi- 
ments were designed and instruments invented to obtain quanti- 
tative results of various types, and the methods followed in the 
formulation of a variety of theoretical postulates, before materials 
suitable for mathematical study were assembled. Till the nine- 
teenth century no parts of science, other than mechanics and 
astronomy, were so highly organized and coherent that the appli- 
cation of mathematics was possible, otherwise than in elementary 
computations. But with regard to mechanics and astronomy the 
second limitation latent in the resources of mathematics itself 
becomes significant; the great achievements which signalized the 
triumph of the scientific revolution would have been impossible 
in the absence of the enormous elaboration of pure mathematics 
which took place, and was to some extent inspired by realization 
of the fact that it was essential. Nearly all the great mathematicians 
of, the sixteenth and seventeenth centuries, from Tartaglia and 
Stevin to Cavalieri, Descartes, Newton and Leibniz, were at least 
partly interested in the physical sciences. One of the unexpected 

1 Pascal deduced that the atmospheric pressure would fall progressively 
above sea-level from his own repetition of Torricelli's experiments with the 
barometer. The deduction was confirmed by P6rier's ascent, with the instru- 
ment, of the Puy-de-D6me, in Auvergne. 


discoveries of the time was that a number of regular mathematical 
curves (some long familiar), such as the ellipse, the parabola and 
the cycloid, or the algebraic functions which Descartes associated 
with such curves, appeared in the investigations of the astronomer 
and the physicist, so that their study proved to have a double 
interest. The calculations performed by the physical scientist fre- 
quently required the calculation of an area bounded by a curve 
of some type, and so in turn stimulated investigation of the opera- 
tion of integration in which perhaps the success of seventeenth- 
century mathematicians was most striking. A number of their 
advances in method were first denoted by the solution of some 
problem in mechanics, which offered from about 1650 onwards 
a most rewarding opportunity for the display of mathematical 
inventiveness, formerly more commonly devoted to the improve- 
ment of the mathematical procedures in astronomy. 1 

The progress made in mathematics in the seventeenth century 
can be very easily illustrated from the fact that, about 1600, it 
had hardly as yet reached a form intelligible to modern eyes. The 
writing of Arabic numerals was indeed nearly stabilized in the 
modern style, but the Roman were still commonly employed, 
especially in accounting. The use of the modern symbols for the 
common operations of multiplication, division, addition and so 
forth was standardized only in the second half of the seventeenth 
century. Previously mathematical arguments were set out in a 
diffuse rhetorical form. Algebraic notation was settled at about 
the same time, the practice of employing letters to denote un- 
known or indeterminate quantities having been introduced by the 
French mathematician Viete shortly before 1600. Arithmetical 
operations, particularly those involving long division or the hand- 
ling of fractions, were still performed by cumbersome methods, 
and "reckoning with the pen" (rather than with the abacus 
or other aid) was still regarded as a somewhat advanced art. One 
of the earliest calculating-devices, the so-called "Napier's bones," 
was designed to obviate the memorization of multiplication tables 
and the labour of handling long rows of figures. Again, at a higher 
level, tables of functions were very deficient. In trigonometry, the 

1 It has been pointed out that almost all the progress made in the theory of 
structures, for instance, before about 1 770, was made as a by-product of sheer 
mathematical ingenuity. The same might be said of the applied science of 
ballistics, which also had a negligible experimental foundation before 1 740. 


Greeks had known tables of chords alone; during the late middle 
ages tables of sines and tangents became available, and during the 
sixteenth century other trigonometrical functions were tabulated. 
But the methods of computing and of using the tables were both 
very tedious. From an attempt to facilitate calculations involving 
these functions developed the invention of logarithms, perhaps the 
most universally useful mathematical discovery of the seventeenth 
century, as it was certainly the least expected. Napier's tables, 
published in 1614 (Mirifici logarithmorum canonis descriptio), gave 
logarithms of sines which are effectively powers of a base e~ l , the 
reciprocal of the base of modern Napierian logarithms. 1 A table 
of logarithms to the base 10 for the first thousand numbers was 
published by Henry Briggs in 1617. Logarithms offered a com- 
pelling instance of the utility of the decimal system of fractions, 
of which Stevin had been a most forceful advocate some thirty 
years earlier. 

Sincefthe Greeks had excelled in geometry and trigonometry, 
little more than the assimilation, with some slight extension, of 
their methods in these branches of mathematics had been accom- 
plished by 1600. Renaissance scholarship had devoted itself to the 
recovery of the pure classical tradition in this as in other depart- 
ments of learning, with the result that the texts, particularly those 
describing the more advanced Greek studies of geometrical analy- 
sis and the conic sections, were far more completely available by 
the middle of the sixteenth century than before. Here, at least, 
pure scholarship caused an immediate rise in the level of com- 
petence. Even in the mid-seventeenth century the practice of 
"restoring" a lost or fragmentary work by means of the methods 
presumably used by the ancient author did not seem absurd, and 
when Newton wrote the Principia the synthetic geometry of the 
Greeks was still held to be a more reliable form of mathematical 
demonstration than the recently developed analytical method. 

Algebra, on the other hand, represents a native European de- 
velopment from Hindu and Islamic sources made known to the 
Latins by medieval translators. Considerable progress in the 
sixteenth century, for example in the solution of equations of 
higher powers than the quadratic, was unaffected by humanistic 
influences; indeed, Greek geometric procedures for solving equa- 
tions were supplanted by algebraic methods. Operations with 
1 Hence log N = 2 30259 Iog 10 fl. 


proportions and series, also known to the Greeks solely in the 
geometric form, were similarly transformed into the more con- 
venient algebraic symbolism. Islamic mathematicians (notably 
Omar Khayyam, c. noo) had recognized a partial equivalence 
between algebra and geometry, that is, that certain geometrical 
problems could be represented by algebraic functions; and this 
equivalence was more thoroughly exploited by the European 
mathematicians of the sixteenth and early seventeenth centuries. 
The next step, upon which analytical geometry is founded, was 
the representation of any function graphically by the use of 
rectangular co-ordinates. Graphs with such co-ordinates had been 
used in the middle ages for a few special purposes (e.g. to repre- 
sent the motions of the planets), and Oresme's calculus of varying 
qualities was itself an elementary form of co-ordinate geometry. 
Far more general and precise methods had been sketched in 
private by the English mathematician Harriot, and by Pierre 
Fermat, before the publication of the first treatise on the subject 
by Descartes the Geometric annexed to his Discourse on Method 
(1637). In this he showed that a constant relationship exists be- 
tween the co-ordinates x and y of any point on a regular mathe- 
matical curve which can be expressed as the algebraic function 
y =f(x) 9 and that certain patterns of function corresponded 
uniformly with certain classes of curves."N 

This discovery was capable of immediate and fruitful applica- 
tion to mechanics, in which many problems could be most easily 
postulated in an initial geometric form, and then analysed with 
the aid of the appropriate algebraic functions. Thus, to cite a 
simple instance, in ballistics it was no longer necessary by the 
end of the seventeenth century to work out a range by supply- 
ing the necessary constants in the geometric construction used 
by Galileo, since it could be obtained directly from the function 


y = x tan e 


appropriate to the parabolic trajectory, from which all the 
theorems established by the elaborate geometry of Galileo and 
Torricelli are readily deduced.Such functions can, of course, be 
derived far more easily bymSe of the differential and integral 
calculus than by the application of algebraic notation to conven- 
tional geometrical reasoning, and the usefulness of the "calculus" 
to the engineer and technician as well as to the mathematical 


scientist has therefore been clearly recognized since about the 
middle of the eighteenth century. Both Kepler (1616) and 
Cavalieri (1635) made use of infinitesimals in integration, the 
former in connection with practical problems such as the calcula- 
tion of the volumes of casks. Thus Cavalieri imagined that the 
area of a surface was made up of an infinite number of lines, and 
the volume of a solid of an infinite number of superposed surfaces, 
calculating these quantities by the summation of an infinite 
number of their geometric elements. Such methods had a certain 
practical value, but the concepts were badly defined and of 
doubtful validity. In co-ordinate geometry the problems for 
which they were designed were first set out in the modern syste- 
matic form. Perhaps even more important were the methods for 
finding the maximum and minimum values of curves (or the 
equivalent functions), and for drawing tangents to them, dis- 
covered by Fermat (1638) and others about the middle of the 
century, for they used operations identical in principle with what 
was later known as differentiation.^ Barrow, for example, in his 
method of tangents, obtained by geometrical means the derivative 

( Jr ) f tne function (j> =/(#)) represented by the curve, and 

equated this derivative to zero. 

(Before 1670, therefore, the crude components of new mathe- 
matical processes for dealing with quantities having a non-linear 
variation were already in existence. The priority in time in 
perfecting them undoubtedly belongs to Newton (whose Method 
of Fluxions was written in 1671), but a more useful notation and a 
somewhat clearer presentation of the matter were later developed 
independently by Leibniz, whose first essay on the calculus was 
published in 1684. The charge maintained by a group of English 
mathematicians, with considerable covert assistance from Newton 
himself, that Leibniz had plagiarized Newton's ideas from un- 
printed manuscripts which had circulated privately provoked in 
the early years of the next century a sordid and bitter dispute 
between them and most continental mathematicians. Its only 
significance is that the transmission to England of continental 
discoveries in pure and applied mathematics was inhibited for 
over a century, until soon after 1830 the Newtonian method of 
fluxions was replaced by the virtually equivalent differential and 
integral calculus which had advanced very far from Leibniz' 


original invention. 1 In principle, both Leibniz and Newton were 
successful in the same task: they generalized the methods of 
differentiation and integration which were already in existence, 
recognizing that the latter operation was the inverse of the former; 
they developed the new notation required for these new opera- 
tions; and they greatly clarified mathematical thinking about 
their nature?\Both succeeding in solving by the new methods 
problems which had been nearly intractable to the old. 

The first coherent treatise explaining the calculus was only 
written at the close of the seventeenth century, and its general 
extension to mechanics and physics was the work of more than 
one succeeding generation. Consequently its full impact on science 
was not immediate, though Newton referred in passing to his 
method of fluxions in the Principia and the mathematical demon- 
strations he offered would have been impossible without it. 
Nevertheless, mathematical methods tending towards those of the 
generalized calculus, or even anticipating it, were widely applied 
in mechanics from about 1650 onwards, along with other new 
developments in advanced algebra (for example, the study of 
series) . Huygens offers perhaps the neatest instance of a physicist 
making by means of co-ordinate geometry many complex calcula- 
tions that would now be dealt with by means of the calculus, 
through the development of his own methods which were virtually 
equivalent to differentiation and integration} In this way Huygens 
was able to investigate some of the properties of motion in a 
resisting medium, which were also examined (rather more 
thoroughly) by Newton in Book II of the Principia with the aid of 
fluxions. It seems that, with the exception of celestial mechanics, 
the development of no branch of science was seriously obstructed 
by the absence of a suitable mathematical technique, even before 
the formulation of the true calculus. Some known problems 
remained unsolved, naturally, partly owing to imperfect concep- 
tualization, but partly also owing to the fact that their solution 

1 The truth seems to be that Leibniz was in close contact with men who 
understood something of Newton's new ideas; that he saw some of Newton's 
manuscripts; but that he could have learned little in this way that he could not 
have gathered from other sources, and that his ideas were already at the 
significant time shaping towards the form in which they were later formulated. 
Leibniz has long been cleared of the charge of plagiarism; any historical 
obscurities that remain are of little significance. (For bibliography cf. D. E. 
Smith: History of Mathematics, vol. II, p. 691.) 


required difficult approximations involving constants which had 
not yet been determined experimentally. On the contrary, it 
seems rather that the nature of the possible mathematical processes 
exercised a powerful guiding influence at least over the science of 
mechanics. Even had ideas been more precise, and the experi- 
mental material more complete, it would have been impossible 
for the seventeenth-century physicist to work out a mathematical 
corpuscular theory of matter because he lacked the necessary 
technique of statistical analysis; but mechanics acquired an 
increasingly theoretical character because its problems could be 
stated mathematically, and solved by known procedures. The 
propositions of the Principia are not less certain, although they 
may not be the result of mathematical analysis applied to a mass 
of experimental data; but it must be recognized that Newton's 
method was to deduce, by mathematics, the consequences of 
selected axioms and then to show by reference to observation or 
experiment that these consequences are actually confirmed in 
nature. Already in Galileo's writings it is apparent that in science 
the mathematical and experimental approaches are far from 
identical, though they may be closely correlated. He himself 
attached greater importance to his mathematical theories than to 
his experimentation (which is never precisely described, and often 
appears casual). The early researches of the scientific societies laid 
a greater emphasis on exactitude and consistency in experiment; 
but mechanics was again sublimated into the regions of higher 
mathematics in the last years of the century !)The consequence of 
this may be illustrated by Huygens' ingenious proof that a pendu- 
lum is perfectly isochronous when describing a cycloidal arc a 
discovery, made with the object of perfecting the mechanical 
clock, which proved completely irrelevant to the experimental 
search for a scientifically reliable time-keeper; or by the history 
of the industrial revolution, which was scarcely at all promoted by 
the elaboration of theoretical mechanics during the eighteenth 
century. There was, in fact, a strong tendency for the first truly 
mathematical branch of science to lose touch with its roots in 
experiment by becoming no more than a specialized department 
of mathematics. 

rit may perhaps seem surprising that seventeenth-century 
mathematics progressed so opportunely as to satisfy, very largely, 
all the demands that science made upon it. Only the activity of 


a number of highly original mathematicians made this possible, 
and obviously their activity was not wholly fortuitous (it is re- 
markable, for instance, that there was so little interest in the theory 
of numbers) . It was inspired, to some extent, by knowledge of the 
usefulness in science of advances in certain directions. But it is 
generally true, of other periods as of this, that the mathematics 
required for any particular step in science has been available. 
Greek science was never near to exhausting the subtlety of the 
Greek mathematician. In recent times the mathematics of the 
theory of relativity was in being well before Einstein. Perhaps this 
empirical fact, more than anything else, justifies the qualification 
of mathematics as a scientific technique. When a class of facts, or 
concepts, is first subjected to its use, the mathematics involved 
will tend to be relatively simple, if only for the reason that the 
innovator will probably be a scientist, more familiar with the 
science than with the most recent advances in mathematics itself. 
Galileo was not a great mathematician. But as the mathematical 
theory develops, its continuance will increasingly depend upon 
the activity of men who have been trained as mathematicians to 
digest and analyse the results of experiment, even to suggest and 
perhaps carry out the experiments and measurements necessary 
for the prosecution of the theory. Yet it will rarely happen that 
the mathematician who applies his skill in this way penetrates to 
the very frontiers of pure mathematics. While the application is 
perfected, mathematics itself is not standing still. And the appli- 
cation is made because the mathematical theorist perceives that 
the particular technique is appropriate, or adaptable, to the 
problem. The conjunction of the highest mathematical with the 
highest scientific ability, as in Archimedes or Newton, is extremely 
rare; the fabrication of scientific theory by the use of well-known 
procedures has, on the other hand, been a frequent occurrence 

The invention of numerous scientific instruments during the 
seventeenth century, and their fertile use in many capacities, has 
long been associated with the revolution in scientific thought and 
method. The idea of science as a product of the laboratory (in 
the modern sense of the word) is indeed one of the creations of 
the scientific revolution. In no previous period had the study of 
natural philosophy or medicine been particularly linked -with the 
use of specialized techniques or tools of inquiry, and though the 


surgeon or the astronomer had been equipped with a limited 
range of instruments, little attention was paid to their fitness for 
use or to the possibility of extending and perfecting their uses. 
More variants of the astrolabe, the most characteristic of all 
medieval scientific instruments, were designed during the last 
half-century of its use in Europe (c. 1575-1625) than in all its 
preceding history. The Greeks had known the magnifying power 
of a spherical vessel filled with water, but the lens was an inven- 
tion of the eleventh century, the spectacle glass of the thirteenth, 
and the optical instrument of the seventeenth. Navigational 
instruments also were extremely crude before the later sixteenth 
century. It was not that ingenuity and craftsmanship were wholly 
lacking (for many examples of fine metal-work, for artistic and 
military purposes, prove the contrary); rather the will to refine 
and extend instrumental techniques was absent. On the other 
hand, it has justly been pointed out that the early strategic stages 
of the scientific revolution were accomplished without the aid of 
the new instruments. They were unknown to Copernicus, to 
Vesalius, to Harvey, Bacon and Gilbert. They leave no trace in 
the most important of Galileo's writings, in which he reveals 
himself driven to measure small intervals of time by a device 
considerably less accurate than the ancient clepsydra. It is clear 
that, great as was the influence of the instrumental ingenuity of 
the seventeenth century upon the course of modern science, such 
ingenuity was not at all responsible for the original deflection of 
science into this new course. 

Thus it would seem that the first factor limiting the introduction 
into scientific practice of higher standards of observation and 
measurement, or of more complex manipulations, lay in the 
nature of science itself. Only when the concept of scientific re- 
search had changed, as it had by the end of the first quarter of 
the seventeenth century, was it possible to pay attention to the 
attainment of these higher standards. A number of the new instru- 
ments of the seventeenth century were not the product of scientific 
invention, but were adopted for scientific purposes because the 
new attitude enabled their usefulness to be perceived. The balance 
was borrowed from chemical craftsmanship. The telescope was 
another craft invention, initially applied to military uses. The 
microscope was an amusing toy before it became a serious instru- 
ment of research. The air pump in the laboratory was an improved 


form of the common well pump Otto von Guericke, its original 
inventor, had at the beginning exhausted vessels by pumping out 
water with which they had been filled. And inevitably the tech- 
niques used in the construction of the new scientific instruments 
were those already in existence; they were not summoned out of 
nothing by the unprecedented scientific demand. Some instru- 
ments were only practicable because methods of lathe-turning 
and screw-cutting had been gradually perfected during two or 
three centuries, partly owing to the more ready availability of 
steel tools, others, because it was possible to produce larger, 
stronger and smoother sheets or strips of metal. The techniques 
of glass grinding and blowing which provided lenses and tubes 
might have been turned to scientific use long before they were. 
The established skill of the astrolabe-maker could be devoted to 
the fabrication of other instruments requiring divided circles and 
engraved lines, that of the watch-maker to various computers and 
models involving exact wheel-work, and so on. Common crafts- 
manship held a considerable reservoir of ingenuity, when scientific 
imagination arrived to draw upon it. 

On the other hand, once interest in the kind of result that could 
be obtained from the employment of specialized instruments had 
been created, particularly as this employment began to extend 
under a more disciplined direction towards a greater qualitative 
depth of information and a greater quantitative accuracy of 
measurement, the limitations of normal craftsmanship were soon 
reached. Then it was necessary to begin a more conscious exami- 
nation of the instruments themselves. Descartes was virtually the 
founder of the scientific study of the apparatus of science, in his 
investigation of the causes of the distortions present in the images 
of crude microscopes. (At the same time, purely empirical measures 
were also being adopted to remedy their defects.) Descartes con- 
cluded that lenses should be ground to a non-spherical curvature, 
which would introduce greater complexity into their manufacture. 
Some scientists (including the astronomer Hevelius, and the 
microscopist Leeuwenhoek) became masters in the art of grinding 
the lenses they required for their work; others, like Newton, 
experimented with an alternative form of optical instrument. 
Towards the end of the century a scientist wishing to have a 
really good telescope or microscope could no longer simply make 
use of craftsmanship; he had to direct the work in accordance 


with a pre-determined specification. Astronomy had already at 
the end of the sixteenth century reached the point where further 
advances in precision involved great effort. Devices like the 
vernier scale and the tangent screw were major steps, and the 
attachment of telescopes to instruments for measuring angles 
reduced sighting errors. But the advantages gained by increased 
complexity in mechanical construction were all dependent on 
progressive refinement in workmanship, and the forethought and 
supervision of the scientist. The astronomer, in fact, had to 
consider his observatory as an exercise in design; he had to build 
walls, duly orientated, that would not settle; to design quadrants 
that were rigid, yet light, and true; to ascertain the probable 
errors of divided scales; to collimate his telescopes and rate his 
clocks. He had become aware that the limitations to his work 
were imposed by factors that were, in the main, technical and 
mechanical. As such, they deserved, and received, increasingly 
meticulous attention. 

From the historical point of view, instruments may be divided 
into two classes: those which render qualitative information only, 
and those which permit of the making of measurements. Naturally, 
these uses of an instrument are not necessarily exclusive, in fact a 
little consideration makes it obvious that in their evolution most 
early scientific instruments tended to move into the second class. 
Thus, devices like the micrometer could be added to telescopes 
and microscopes so that very small or very distant objects could 
be measured; or alternatively these optical systems could be added 
to other measuring instruments to improve their performance. 
But the first use was purely qualitative. Similarly, in the eighteenth 
century, the electrometer designed in the first place for the detec- 
tion of charges, was later applied to their comparison and measure- 
ment. The balance was first used in chemistry to establish a simple 
loss or gain in weight; its employment to determine accurately 
the masses involved in a chemical reaction came much later. 
It is therefore a natural and plausible proposition that the quanti- 
tative potentialities of a new instrument or piece of apparatus are 
generally appreciated less readily than the qualitative, and this 
was particularly the case in the seventeenth and eighteenth 
centuries. The invention of instruments, therefore, did not have 
that immediate effect of inducing greater rigour, and greater 
interest in refined measurement, which might be anticipated a 


priori. The barometer, for example, was invented by Torricelli 
in 1643. ^ was use d originally to demonstrate the existence of 
atmospheric pressure, and secondly as a means of exhausting a 
small chamber formed at the top of the tube in which experiments 
could be made. Only about 1660 was the correlation between 
barometric pressure and climatic conditions discovered, and only 
after this were attempts made to improve the readability of the 
instrument and collect a " history of the weather." Later still, 
Boyle employed the barometer as a gauge to measure the quality 
of the vacuum formed by his air-pumps, and the amount of "air" 
evolved from fermentations. The thermometer has an even longer, 
and more surprising, history as a merely qualitative instrument. 
The thermoscope, an instrument in which the expansion of air in 
a bulb moved a column of water in a narrow tube upwards when 
heat was applied, was invented by Galileo about 1600. Liquid 
thermometers were introduced about the middle of the century, 
and were extensively used by the Accademia del Cimento, but 
none of these was calibrated. The first suggestions for systematic 
calibration with the use of two fixed points were made about 1665; 
Fahrenheit's scale was devised about fifty years later, and the 
modern centigrade scale only in 1743. Thus the first century of 
thermometry yielded no quantitative measurements which can 
now be interpreted with any degree of confidence. 1 

While seventeenth-century astronomers, continuing a long 
tradition, effected a refinement of angular measure which bore 
fruit in Flamsteed's Historia Coelestis Britannica (1725), in physics 
and biology qualitative results were far more significant. Even the 
allied science of terrestrial angular measure (in surveying and 
geodesy) remained rather crude until vernier scales and telescopic 
sights were introduced at the close of the century. Consequently 
it can scarcely be maintained that technical limitations to accuracy 
of measurement were significant in any other branch of science 
than astronomy before the early part of the eighteenth century. 
Certainly it has been argued that chemistry would have pro- 
gressed faster, and the science of heat have been more systematic, 
if greater attention had been paid to the quantitative aspects of 

1 The tubes of the early thermometers were of course divided, so that 
comparative readings could be taken, but without reference to any standard 
scale. Thus, extensive observations were rendered useless by the fact that they 
depended on the arbitrary divisions of a unique instrument. 


experiment; but the reasons for the neglect of these aspects are to 
be sought rather in the nature of scientific activity in the seven- 
teenth century, than in instrumental deficiencies. The importance 
of accurate measurements was not adequately understood, and 
therefore they were rarely made; so that it was the texture of 
science that hindered the effective exploitation of devices already 
in being, rather than vice versa. 

On the other hand, with regard to the two qualitative instru- 
ments which most strikingly opened up great new fields of activity, 
the telescope and microscope, it is plain that technical limitations 
rapidly became serious, and that the nature of these limitations 
was well understood. Both instruments began in very crude form. 
Systems of convex lenses replaced the concave-convex combina- 
tion (the so-called Galilean arrangement) only gradually from 
about 1640, when rules for working out the appropriate focal 
lengths and apertures were better understood. The first true com- 
pound microscopes date from about this period, and the new 
(Keplerian) telescope brought more detail of the solar system into 
visibility. Additional satellites were discovered; the mysterious 
appearance of Saturn was accounted for; transits and occultations 
could be observed with higher accuracy. But the great desideratum 
of seventeenth-century astronomy an observational proof of the 
earth's rotation was not accomplished. To increase magnifica- 
tion without a corresponding vitiating increase of the aberrations 
the astronomer was compelled to use very long focal lengths and 
small apertures. The light-gathering power of such instruments 
was poor, and a practical limit to length (about 100 feet) was soon 
reached. Non-spherical curvatures for lenses were theoretically 
desirable, but technically impracticable. Newton's optical theory 
explained the nature of chromatic aberration without suggesting 
an appropriate remedy, for he found that the separate colours 
into which white light can be resolved could not be brought 
to a single focus by a simple lens. The reflecting telescope, free 
from chromatic aberration, was suggested by James Gregory 
and first constructed by Newton, but it was hardly of serious 
value to astronomers before the later years of the eighteenth 

Similar problems were encountered in the microscope. Simple 
glasses, with a magnification of about ten diameters, were used 
early in the seventeenth century; by Harvey, who observed the 


pulsation of the heart in insects, and by Francesco Stelluti who 
published in 1625 a microscopic study of bees. The small tubular 
" flea-glass," with the lens mounted at one end, and the object set 
against a glass plate at the other, became popular among the 
virtuosi. Towards the middle of the century the compound micro- 
scope attracted renewed interest, being now constructed with a 
bi-convex objective and eye-lens, with a plano-convex field lens 
placed between to concentrate the rays. In the improved design 
of Hooke (described in Micrographia y 1 665) the body, containing 
extensible draw-tubes, was mounted so that it could be tilted to a 
convenient angle; a long nose-piece engaged in a large nut, so that 
the body could be brought to focus on the object by screwing it in 
or out. The lead-screw and slide method of adjustment was in- 
vented later by Hevelius. To illuminate opaque objects Hooke 
used an oil-lamp and bull's-eye lenses; before the reflecting- 
mirror was fitted (about 1720), transparent objects were examined 
by placing a lamp or candle on the floor beneath the instrument, 
which was often pierced through the base. The compound micro- 
scope was complicated and expensive, but it was easy to handle, 
and in mechanical design became steadily more efficient. Optically 
it was less satisfactory. Magnifications exceeding 100 diameters 
could be obtained, but the uncorrected lenses, made of poor glass, 
gave low resolution. As a result, the point was soon reached where, 
though the object could be made to appear larger, no finer detail 
in it could be seen. From 1665 until about 1830, when satisfactory 
corrected lenses became available, the compound microscope 
made comparatively slight advance in optical properties. The 
limitation imposed, on biological research in particular, is obvious. 

Nevertheless, the compound microscope was eminently a scien- 
tific instrument, and Hooke's Micrographia the first treatise on 
microscopy. Since his objects were fairly coarse (insects, seeds, 
stones, fabrics, a razor's edge, leaves, wings, feathers, etc.), and 
since he did not seek to penetrate into anatomical structure by 
dissection (though he examined the compound insect eye, and 
discovered the cellular composition of cork) he was able to produce 
a series of admirable illustrations despite the limitations of his 
microscope. Most of the discoveries of the time in minute ana- 
tomy, associated with the names of Malpighi, Swammerdam and 
Grew, such as the capillary circulation of the blood, could also be 


demonstrated with the compound instrument. 1 For the very finest 
observations, however, another technique was required, in which 
the Dutch microscopist Antoni van Leeuwenhoek excelled. The 
compound microscope had stimulated the grinding of very small 
bi-convex lenses of short focal length for use as objectives. It was 
found that better results could be obtained by mounting such high- 
power lenses, or even tiny fused glass spheres, as simple micro- 
scopes than by using them as elements in an optical system that 
multiplied the aberrations. For considerable magnification the 
lenses had to be less than one-tenth of an inch in diameter; they 
were proportionately difficult to grind and manipulate, and they 
imposed severe eye-strain. But Leeuwenhoek reported, in his 
letters to the Royal Society, observations obtained by this means 
which were only repeated with the achromatic microscopes of the 
nineteenth century. His skill as an optician is further shown by the 
fact that one of his few surviving lenses has been proved, by recent 
tests, far superior to any other known simple lens; others of his 
own make are good but not outstanding. This skill enabled him to 
study more thoroughly than any other observer spermatozoa and 
the red corpuscles in the blood and to become the first to discern 
protozoa and bacteria. Despite some contemporary incredulity, 
aroused by the great number and disparity of Leeuwenhoek's 
original discoveries, and the difficulty of confirming them, his 
work was astonishingly accurate. He was also creditably free from 
the tendency to theorize, or to allow his imagination to play with 
his microscopic images. At the end of the century Leeuwenhoek 
was alone in his investigation of microscopic creatures, although 
others were engaged on the study of the microscopic parts of 
larger creatures; his results, therefore, remained largely isolated 
curiosities. In the eighteenth century the description of various 
animals, visible to the naked eye but capable of being studied only 
with the aid of the microscope, was taken up both in England 
(Baker, Ellis) and in France (Reaumur, Bonnet, Lyonet) . Tremb- 
ley, whose monograph on the hydra has become a classic, worked 
in Holland and was closely associated with both the English and 
the French groups of naturalists. All these worked with the simple 
microscope but at a much lower magnification than that frequently 
employed by Leeuwenhoek. This instrument thus became estab- 
lished in familiar use among zoologists and botanists for much the 

1 See below, p. 286. 



same purposes as it serves at the present time, when the higher- 
powered compound microscope, given a beautiful mechanical 
construction by the English instrument-makers, was still of little 
scientific value. The continuation of the sciences of histology and 
cytology, begun by Malpighi and Leeuwenhoek, depended upon 
the perfecting of lenses which proceeded swiftly in the early 
nineteenth century. 

It would be possible to develop other, comparable, instances 
of the way in which, after an initial seventeenth-century invention, 
a long interval followed before, in a stage of higher proficiency 
in instrumental techniques, observations or measurements of a 
different order became practicable. The Newtonian reflecting 
telescope, with Herschel's improvements, for the first time enabled 
the astronomer to escape the confines of the solar system. If the 
" chemical revolution" of the eighteenth century was effected 
without profound modifications of apparatus, on the other hand 
the chronology of electrical science was fixed by the discovery of 
instruments for the creation, and the measurement, of charges and 
currents. These in turn induced new chemical techniques, such 
as electrolysis. During that century a considerable literature grew 
up dealing with the manufacture and use of scientific instruments 
of all kinds, and teaching the technique of making experiments 
and observations, while the actual manufacturers strove intelli- 
gently to improve their wares. John Dollond, the practical man 
who solved the problem of making achromatic telescope objectives 
which had baffled mathematicians, was an instrument-maker. 
The marine chronometer, in the perfecting of which so much was 
due to another practical man, John Harrison, imposed a close 
collaboration between watch-makers and astronomers. Science, 
therefore, entered into a promising situation with the early nine- 
teenth century, being able to call upon the services of a skilful 
and progressive specialized craft, and realizing far more perti- 
nently than hitherto its own dependence upon its material equip- 
ment. In nearly every respect its progress was involved in that of 
some instrument, or in that of a variety of laboratory techniques. 

Because a three-fold division of function may exist in science, 
between the instrument-maker, the laboratory worker' and the 
theorist, it has always been possible, and still is, for the strategic 
thinking in science to take place outside the laboratory, away from 


the instruments (though it may still be controlled by the accessible 
mathematical techniques). Thus Tycho's instruments were made 
by the metal-workers of Augsburg; he himself managed their use 
with consummate skill; and his results were interpreted by the 
mathematician Kepler. But the third function without the second, 
and the second without the first, can clearly yield only diminishing 
returns. The progress of science demands originality at all three 
levels; more than this, it may demand the existence of resources 
of industrial magnitude, of a glass-industry, a gas-industry, of the 
great plants required to produce antibiotics and radio-active iso- 
topes. If it seems increasingly likely that the major advances of 
the future will come from large institutes, freely endowed, and as 
the result of co-operative labours, it is no more than a fresh step 
in that growth of complexity, and of an increasing reliance on 
techniques and tools of investigation, which was typical of the 
scientific revolution. In a sense it is the fulfilment of Bacon's 


IT might be misleading to suggest that the career of Isaac 
Newton represents the peak of the scientific revolution, the 
point at which the transition from renaissance to modern 
science became complete. The qualifications to be added to such 
a generalization are obvious. Profound changes in the methods 
and theories of the non-mathematical sciences, upon which the 
impact of Newton was negligible, were deferred to future times. 
He showed no interest in biology; perhaps, indeed, to his highly 
organized intellect its structure was wholly alien. It could be 
argued that Newton's essentially physical approach to chemistry 
was no less a departure from the traditions of that science than 
Lavoisier's theory of chemical combination, but Newton's ideas, 
despite their surviving historical interest, proved unconstructive. 
Their ingenuity was premature, and Newton, like Boyle, in his 
treatment of chemistry as a branch of corpuscular physics more 
nearly resembled an ancient philosopher than a nineteenth- 
century chemist. The clear light shining through his mathematical 
and physical researches did not illumine other, darker quarters of 
Newton's mind and character. The author of the Principia was 
also the compiler of millions of words of extracts from the most 
obscure alchemical writers; the great mathematician laboriously 
computed the generations that had passed since the creation of the 
world. Despite his genius, despite his rapid and sure mathematical 
invention, despite his experimental precision, science was always 
for Newton a detached intellectual pursuit, not an activity, a 
cause, close to the emotional core of his being. Strangely, to 
modern ways of thinking, alchemy seems to have given him a 
greater sense of the ultimate mystery than his unfolding of the 
celestial system. To many of the critical issues of the scientific 
revolution he was insensitive. Unlike Descartes or Boyle he felt 
impelled to utter no fundamental pronouncements on the trinity 
of God, Nature and Man. Cutting neatly and narrowly through 
the froth swelling up from the intellectual ferment of his age, 
withdrawing himself from idealists and propagandists, the social, 



religious and philosophic implications of the scientific revolution 
scarcely touched him. Newton saw the ideal of scientific truth se- 
renely, as an end attainable by the application of methodical prin- 
ciples; it provoked in him no warm revulsion against established 
errors, no enthusiasm for a hopeful shift in the course of civilization. 

Even Newton, therefore, cannot be described without reserva- 
tion as a "modern scientist." His own attitude to nature still bore 
traces of the medieval; he faced some problems which the modern 
world considers unworthy of serious consideration, and by con- 
trast philosophized sometimes in such a fashion as to gloss over 
other problems which have since become important. Nevertheless, 
Newton's contributions to those branches of physical science that 
were studied in the seventeenth century mark a peak of achieve- 
ment. At the same time they disclosed fruitful prospects for the 
future advance of science, but where the influence of Newton was 
most profound in the theory of gravitation, in the theory of 
light, and in the particulate theory of matter his own example 
was so commanding, and his own explorations were of such range, 
that for about a century no investigation passed the limits of the 
Newtonian framework. Newton may be pictured as establishing 
developing sciences at a new level, less by seeing the problems in 
ways unimagined by his contemporaries than by the exercise of 
his greater ability and mathematical skill. At about this level they 
remained until the nineteenth century was well advanced, while 
the major creative impulse was transferred to the less organized 
departments of science, to chemistry and biology, and in physics 
to the study of heat and electricity. The comparative stagnation in 
the eighteenth century of those aspects of physics which had seen 
most revolutionary developments in the seventeenth is a measure 
of Newton's success in extracting the quintessence of knowledge 
from those scientific procedures which the seventeenth century had 
developed most highly; for long it seemed that in those aspects 
no other procedures, and no greater knowledge, were possible. 

The Newtonian theory of light was severely shaken by Young 
and Fresnel about 1820, and at the same time a notion of electrical 
attraction among the ultimate particles of matter was gradually 
replacing the Newtonian idea of a gravitational attraction. These 
were the first checks to the established structure of physics, while 
serious doubts of the inviolability of Newtonian or classical 
mechanics only arose at the very end of the nineteenth century. 


Throughout a long period of more than 150 years Newton's 
scientific thinking in mathematical science appeared practically 
infallible; other aspects of his intellect were still almost completely 
hidden, partly owing to the caution of his literary executors and 
editors, who carefully marked so many of his manuscripts as 
"Not fit to be printed," partly owing to Newton's own reticence in 
publication. 1 Before 1684 Newton was a comparatively unknown 
professor of mathematics in the University of Cambridge; his 
optical experiments and construction of a reflecting telescope, 
with his mathematical discoveries which were known only to a 
limited circle, had given him a certain repute, but he had won 
no striking acclaim. The publication of the Mathematical Principles 
of Natural Philosophy in 1687 immediately gave him enormous 
prestige. The Royal Society recognized something of its majesty 
even before the book was printed; foreigners, though more reluc- 
tant to accept Newton's theories, were quick to perceive the genius 
which had given them a mathematical dress. The tone was set by 
Edmond Halley's opening ode to the volume whose publication 
he generously undertook : 

. . . Talia monstrantem mecum celebrate camaenis, 
Vos o caelicolum gaudentes nectare vesci, 
Newtonum clausi reserantem scrinia veri, 
Newtonum Musis charum, cui pectore puro 
Phoebus adest, totoque incessit numine mentem; 
Nee fas est propius mortali attingere divos. 2 

A somewhat fulsome adulation was maintained by English writers 
to recent times (e.g. in Brewster's Life of Newton, 1855); others 
were more critical in equally sincere admiration. Even today the 
distinction between that which was of permanent value in 
Newton's scientific thinking, and that which was stamped with 
the character and preconceptions of his age, is not always very 
clearly indicated. The fact is (as might be expected) that in their 
manifold and complex aspects Newton's contributions even to 

1 Most of his works appearing in his life-time, other than the Principia, the 
papers in the Philosophical Transactions, and the Opticks (delayed until after 
Hooke's death), were first printed without his consent. 

2 *O you heavenly ones who make merry on nectar, celebrate with me in 
song the revealer of these things, Newton to the Muses dear, Ne\yton who 
unlocked the barred treasure-chest of Truth: Phcebus is in his pure breast, and 
enters his mind with all his own divinity. Nearer the Gods no mortal may 


mathematics and mathematical science were not all equally useful, 
though all were important. Newtonian mechanics, and his 
celestial system, have stood firm within limits which are now 
clearly defined; but of the remainder of Newtonian science the 
last century has left scarcely a vestige. 

Clearly Newton, like most great men, was fortunate in the hour 
of his birth: in 1642, the year of Galileo's death. His adolescence 
was accompanied by the foundation of scientific societies, the 
practice of systematic experiment, the gestation of modern mathe- 
matics. In 1665-6 the rather unpromising, and certainly ill- 
grounded student upon whom Barrow had enforced the study of 
Euclid's Elements was in the "prime of his age for invention." 
How much the fruit of his originality owed to the ground from 
which it sprang, to Barrow, to Wallis, Slusius, Kepler, Borelli, 
More, Boyle, Descartes and others whom he read in those early 
Cambridge years! 1 How many, and how rich, were the threads 
which these giants led to the hand of so able a spinner of theorems, 
so close a weaver of theories! The genius that was frustrated by the 
dense mysteries of chemistry reaped a splendid harvest in the 
riper fields of mathematical science in which its fullest powers 
could be exercised. It is no detraction from Newton's originality 
to point out that all his discoveries were firmly rooted in the science 
of the time that like a helmsman he was borne along by the 
stream that each of them has a quality of inevitability in its 
contemporary context. Newton, in fact, won such immediate 
esteem because he saw clearly the things to which others were 
groping, because he was so fully in harmony with his age. Not 
scientists and mathematicians alone, but philosophers and theo- 
logians could find in Newton exactly that of which they wished to 
be assured. Even in his political allegiance to a limited Protestant 
monarchy, in his ambition to rise in the great world of affairs, 
and in his shrewd financial sense, Newton was a good and success- 
ful citizen of Augustan England, a bon bourgeois when the middle 
classes were rising to luxury and power. 

There are no singularities in Newton's early years. As a student 
in Cambridge, he was fashionably inclined to scepticism of the 

1 One would naturally like to add the name of Galileo to this list, but there 
seems to be no evidence that Newton met Galileo in the original, at least at 
this time. 


Cartesian system, looked favourably upon hypotheses of atoms 
or corpuscles, and developed a mild academic interest in the 
empirical method represented by Boyle. Starting rather late, he 
rapidly assimilated the latest mathematical knowledge, but 
although his notebooks show him at the age of twenty-three 
already deeply interested in science, they contain no sketch of 
an original contribution, no hint of a sudden revelation of the 
importance of natural knowledge. He was always apt, much later 
in life, to regard science as an importunate mistress, to work with 
immense concentration and speed upon a problem when the 
passion to solve it fell upon him, because a part of himself doubted 
the problem's cosmic significance. Then, for the better part of 
two years after he had taken his degree, Newton was forced into 
retirement at his country home in Lincolnshire by the plague 
which raged in the towns and villages during 1665 and 1666. He 
had already begun his optical experiments (which seem to have 
been prompted by undirected curiosity, rather than by any 
clearly perceived ambition), and his mind was turning towards 
new conceptions in mathematics. In the winter of 1664-5 he had 
found the method of infinite series, and shortly after discovered the 
binomial theorem; in Lincolnshire during the following summer 
he calculated a hyperbolic area to fifty- two places of decimals; 
in November of the same year he had formulated the direct 
method of fluxions (differentiation), and in May 1666 he began 
upon the inverse method (integration) . During the whole of 1 665 
he must have been working at his optical experiments, and trying 
to grind lenses of non-spherical curvature, and early in 1 666 he 
"had the Theory of Colours." This quickly directed him to the 
construction of his first reflecting telescope. 'And the same year/ 
wrote Newton long afterwards, 'I began to think of Gravity 
extending to y 6 orb of the Moon, & (having found out how to 
estimate the force with which a globe revolving within a sphere 
presses the surface of the sphere), from Kepler's rule ... I deduced 
that the forces which keep the Planets in their Orbs must [be] 
reciprocally as the squares of their distances from the centers 
about which they revolve.' To this period belongs the famous 
story of Newton and the Apple, told at first hand by Newton's 
younger friend, William Stukeley: 

After dinner, the weather being warm [the date was 15 April 1726], 
we went into the garden and drank thea, under the shade of some 


appletrees, only he and myself. Amidst other discourse, he told me, 
he was just in the same situation, as when formerly, the notion of 
gravitation came into his mind. It was occasioned by the fall of an 
apple, as he sat in a contemplative mood. Why should that apple 
always descend perpendicularly to the ground, thought he to himself. 
Why should it not go sideways or upwards, but constantly to the 
earths centre? Assuredly, the reason is, that the earth draws it. There 
must be a drawing power in matter: and the sum of the drawing 
power must be in the earths center, not in any side of the earth. 
Therefore does this apple fall perpendicularly, or towards the center. 
If matter thus draws matter, it must be in proportion of its quantity. 
Therefore the apple draws the earth, as well as the earth draws the 
apple. That there is a power, like that we here call gravity, which 
extends itself thro the universe. l 

When the plague had subsided, Newton returned to Cambridge, 
presumably in the hope (which was soon fulfilled) of becoming a 
Fellow of Trinity College; in 1669 he succeeded Isaac Barrow in 
the Lucasian Professorship of Mathematics. He was now com- 
fortably established in a life that was to be his for nearly thirty 
years. Professorial pupils were few, though Newton must have 
done some college teaching; he had ample leisure for his experi- 
ments in optics and chemistry, and for his mathematics. In 1672 
letters written to Oldenburg, describing the new theory of colours, 
brought him into the Royal Society but the disputes and criticisms 
which followed during the next four years (aggravated by the 
officiousness of Oldenburg) persuaded Newton virtually to cut off 
this connection. His interest in alchemy and chemistry quickened; 
the wooden staircase leading from his first-floor rooms to the 
furnace in the little garden below was shaken by his eager tread. 
It was Halley who brought Newton back into the scientific move- 
ment, who encouraged his interest in mathematical matters, and 
was the godfather of the Principia. The book was begun towards 
the end of 1 684, and was finished by the spring of 1 686. Thereafter 
Newton's life became more full of incident, and more empty of 
science. He took part in the resistance to the Catholic policy of 
James II; sat (silently) as a Member of Parliament; and sought 

1 William Stukeley: Memoirs of Sir Isaac Newton's Life, ed. by A. Hastings 
White (London, 1936), pp. 19-20. Stukeley was forty-five years junior to Newton, 
who was in his eighty-third year in 1 726, and did not compose his memoir until 
1752. His expressions, therefore, cannot be taken very strictly as interpreting 
Newton's state of mind in 1665-6. 


to become Provost of King's College. 1 His fame, and his new 
acquaintance with John Locke, made him known personally to 
men who possessed political power and influence. The prospect of 
exchanging academic seclusion in a provincial town for an office 
of honour and profit in London was welcome. The initial frustra- 
tion of this ambition, working in a mind intolerant of opposition at 
a time when it was strained by overwork, caused a serious break- 
down during 1693. After some months Newton recovered his full 
intellectual powers, but it is to be doubted whether his judgement 
of men's actions ever regained a normal balance. 2 This illness 
brought his creative scientific work to a close. Honours and fame 
came later; in 1696 Newton left Cambridge to become first 
Warden, then Master of the Royal Mint; in 1703 he was elected 
to the Presidency of the Royal Society, which he held for the rest 
of his life; in 1705 he was knighted. In the Augustan Age Newton 
and Pope ruled the intellectual world with a sway more absolute 
than that of the Queen herself. 

That branch of science in which Newton had first published 
original discoveries was also the last to be enriched by his mature 
reflections. The bulk of the Opticks of 1704 had long been written, 
but the Queries with which the book concludes represent Newton's 
final contribution to science, and perhaps the sum of his perception 
of nature. In the Queries optical phenomena are discussed in order 
to throw light on the ultimate particulate structure of matter: 

Have not the small Particles of Bodies certain Powers, Virtues, or 
Forces, by which they act at a distance, not only upon the Rays of 
Light for reflecting, refracting and inflecting them, but also upon 
one another for producing a great Part of the Phenomena of 
Nature? 3 

1 Newton's extraordinary mastery of detailed argument is well revealed in 
the legal briefs that he drew up for the royal benefit to confute the contentions 
of the Fellows of King's. His claim brought him into touch with Christiaan 
Huygens, whose brother Constantyn had come to England in the service of 
William III. It is pleasant to think of these two great, and very different, 
scientists setting off in a coach to petition their common sovereign to promote 
Newton in the academic hierarchy. 

2 Newton's mental illness was a definite paranoia, in which he accused his 
closest friends of persecuting and calumniating him. Locke, in 1705, privately 
described him as 'a little too apt to raise in himself suspicions where there is no 
ground'; this mental trait, which he always had, was played upon by men of 
greater ambition than discretion in the quarrel with Leibniz, wherein INewton 
lost all sense of proportion and probity. 

8 Opticks, Bk. Ill, Qu. 31. 


Newton, indeed, for the first time made optics a branch of physics, 
by his demonstration that the theory of light and the theory 
of matter were cognate and complementary. Before the mid- 
seventeenth century the science of optics was almost wholly geo- 
metrical, and it is interesting that progress was achieved through 
renewed attention to its qualitative aspects. Since the character- 
istic colours of bodies and pigments had long been regarded as 
true Aristotelean qualities, confusion followed upon the challenge 
to Aristotle's philosophy in the time of Galileo. The prismatic 
colours also had long been familiar; in the middle ages an increas- 
ingly more perfect account of the formation of the colours in the 
rainbow had been given by the Latin writers who, following 
Alhazen, regarded them as produced by the refraction of sunlight 
in shining through rain-drops. The geometrical optics of the rain- 
bow were further perfected by Descartes, who also put forward a 
new and more definite corpuscular hypothesis of light. In his view, 
light was a sensation caused by pressure of the matiere subtile on the 
optic nerve, set up by the tendency of this matter to expand in all 
directions from its concentration in the luminous source; colours 
were caused by rotations of the particles of the matttre subtile. 

This was, like all the science of the Principles of Philosophy, an 
unsupported hypothesis. Descartes assumed that light travels 
more rapidly in a dense medium (such as water) than in air, and 
from this the sine-law of refraction could be deduced; but the same 
law could also be deduced from the contrary assumption. There 
was no method of proving either by experiment. The explanation 
of what happens to "light" itself when a beam of white light is 
converted into a beam of one or more colours was vague and 
wholly speculative. In all theories before Newton's, a qualitative 
change in the nature of the beam was suggested, a modification 
of the physical entity of light, which at least in imagination could 
be reversed, so that as red light can be derived from white, white 
ought to be derivable from red. The same potential reversibility 
is implicit in the more ingenious theory of colours described by 
Robert Hooke in Micrographia (1665). Hooke was the first investi- 
gator of the colours produced by optical interference in the form 
known, somewhat unjustly, as "Newton's rings," which he ob- 
served in the laminations of mica, and in plates of glass pressed 
together, finding that the manifestation of the colours depended 
upon the existence of a very thin refracting medium, each colour 



corresponding to a determinate thickness. According to Hooke, 
the sensation of light is caused by a very rapid, short vibrating 
motion in the transmitting medium, every pulse or vibration of 
the luminous body generating a sphere 'which will continually 
increase and grow bigger, just after the same manner (though in- 
definitely swifter) as the waves or rings on the surface of the water 
do swell into bigger and bigger circles about a point of it, where, 
by the sinking of a stone the motion was begun.' Therefore, each 
successive pulse or vibration may be considered as being at right 

angles to the direction of pro- 

AIR , natation radially from the 

(less easy transmission) . , T 

' ' centre, and in a narrow beam 

of light each pulse as a plane 
surface perpendicular to the 
beam. 1 

Hooke next investigated 
geometrically the results of the 
passage of the beam from one 
medium into a second which 
is capable of transmitting the 
pulses more, or less, easily than 
the first. He reasoned that if 
the light falls obliquely upon 
the surface separating the two 
media, one "edge" of the 
pulse (treated as a plane) 

(more easy transmission) 

FIG. 8. Hooke's Theory of Refraction. 
aaabbb, incident ray; cccddd, refracted 
ray. ab, ab perpendicular pulses, cd, 
cd oblique pulses. 

would enter the second medium before the other, and would 
therefore be accelerated or retarded before the latter, in turn, had 
started to travel through the second medium (Fig. 8). He assumed 
(without proof) that when the second medium transmitted the 
pulses more easily the beam would be refracted towards the per- 
pendicular, and consequently that water transmits more easily 
than air. 2 This refracted ray, moreover, would be distinguished 
from the incident ray in that the pulses would now be oblique, 

1 Micrographia, pp. 55-7. 

2 In this Hooke followed Descartes. Fermat had already demonstrated that 
refraction towards the perpendicular occurs when the velocity of light in the 
second medium is less, i.e. when like water or glass it transmits light less easily 
because it is more dense than air. Huygens, in the Traitt de la Lumtire (1690) 
wherein he follows Fermat, by introducing the conception of the wave-front 
into the pulse-theory showed that the sine-law of refraction followed from it. 


not perpendicular to the ray, due to the acceleration or retarda- 
tion of the "leading edge" of each pulse. 1 To this obliquity of the 
pulse Hooke traced the sensation of colour, on the grounds that in 
a whole beam of light there would be some confusion of the oblique 
pulses, and that one "edge" of each pulse would be weakened or 
blunted through having to initiate the vibration in a medium at 
rest; thus: 

Blue is an impression on the Retina of an oblique and confus'd pulse 
of light whose weakest part precedes, and whose strongest follows. 
Red is an impression on the Retina of an oblique and confus'd pulse 
of light, whose strongest part precedes, and whose weakest follows. 

For example, in Fig. 9, towards a the leading edge of each oblique 
pulse, being adjacent to the un- 
disturbed medium, is weakened, 
whereas towards d the lagging 
edge pulse is weakened for the 
same reason. Hence the colour 
blue will be seen about a, and red 
about d. Hooke thought that 
the intermediate colours of the 
spectrum 'arise from the com- 
position and dilutings of these 

two' produced by the confusion , _ u , 

~ * . r FIG. 9. Hooke s Theory of Colours, 

ot the two primary types of 

oblique pulse towards the middle of the refracted beam. He 
further showed by a very ingenious analysis that when a ray 
passes through a very thin medium a similar succession of strong- 
weak or weak-strong pulses is created, according to its thickness, 
producing colours. 

In this theory of light, Hooke devised a subtle mechanism by 
which colours might be derived from white light considered as a 
train of uniform and homogeneous pulses. It accounted for the 
association of heat, light and motion in a crudely sketched kinetic 
theory; for the fact that refraction is always accompanied by 
coloration; for the order of the colours as produced by refraction 
or by interference; and for the fact that the spectrum produced by 
one prism can be re-converted into white light by a second. On 

1 Huygens (see note 2, above) avoided this supposition of obliquity by 
different reasoning on the formation of the refracted wave-front. 


the other hand, it was not very clearly conceived in detail, and it 
explained only a selection of the known facts. Hooke seems to 
have observed that the two sides of a refracted ray are not parallel, 
but makes no mention of the fact (cf. Fig. g). 1 Probably no experi- 
ments on homogeneous coloured light were made by him, since 
he seems not to have known that further refractions have no effect 
upon such light; this would certainly have been difficult to recon- 
cile with his theory. The most serious objection against its broad 
form was that it failed to account for the rectilinear propagation 
of light. If a ray was a train of pulses, why did not these spread out 
into the surrounding medium, as sound-waves do? This was, in- 
deed, for long a profound objection against any pulse or undula- 
tory theory, having been thoroughly discussed by Newton in the 

So far the theory of light had been illuminated by few new 
experiments, and none that were decisive. The ideas of Descartes 
and of Hooke could have been as well propounded in the four- 
teenth century as in the seventeenth. The new experimental evi- 
dence, relating to interference (Hooke) and diffraction (Grimaldi, 
also 1665) seemed to favour the pulse hypothesis, but though the 
two opposed theories were equally mechanical in character, they 
were nevertheless ad hoc hypotheses, entirely lacking in the demon- 
strative solidity on which the "new philosophy" was supposed to 
be founded. By introducing imaginary mechanical qualities of 
pellucid matter, the old Aristotelean theory of colour as a quality 
had only been pushed back to a further remove. Newton's experi- 
ments began where the theories of Descartes and Hooke, with 
which he must certainly have been acquainted, ceased in new 
experiments. His papers in the Philosophical Transactions, containing 
his new theory of prismatic colours, are hardly more than the 
statement of experimental results. The deductions he drew were 
simply those enforced by the new evidence. 

His first paper begins with the observation that a parallel beam 
of white light diverges into the spectrum when it is refracted by 
a prism. The spectrum is longer in one direction, not of the same 
shape as the aperture through which light is admitted. This must 
have been noticed often, and disregarded. Both in the Opticks, 
and in his note-book, however, Newton first describes another 

1 This is shown in Fig. 2 of Schem. VI of Micrographia, where, however, the 
incident ray is shown as convergent though Hooke purports to be using sunlight. 


experiment, in which he observed a continuous line, painted in 
two colours, through the prism and found that the image of the 
parti-coloured line was no longer rectilinear. Perhaps this gave him 
the first clue to what followed. These simple experiments taught 
Newton that 'y e rays which make blew are refracted more y n y c 
rays which make red,' 1 or as he phrased it after many more ex- 
periments described in the Opticks, 'the Sun's light is an hetero- 
geneous Mixture of Rays, some of which are constantly more 
refrangible than others.' Any refracting agent, such as a prism, 
simply acted like a filter to distinguish the infinite components of 
white light according to their refrangibility. Therefore, he thought, 
it was necessary to give up all hope of contriving a lens which 
would refract all colours equally, and so yield an achromatic 
image. Newton was careful to prove that monochromatic light has 
all the optical properties that were " vulgarly" attributed to white 
light, and that there could be no question of the white ray being 
actually shattered by refraction it was merely divided, and it 
could be reassembled. Each pure coloured constituent, however, 
was homogeneous and indivisible. 

This doctrine appeared very shocking to contemporaries. The 
simple nature of white light had always been accepted as axio- 
matic. The proof that all the colours of the spectrum are equally 
primary and necessary in white light cut directly across notions 
which supposed them the product of mixtures of red and blue, or 
blue and yellow. While some theorists of empiricism welcomed 
Newton's Baconian use of experiment, many who prided them- 
selves on their knowledge of optics were hostile. The reactions of 
the critics, Hooke and Huygens amongst them, are interesting. 
When Newton's first paper appeared in the Philosophical Transac- 
tions, they judged initially that he was merely speculating, and 
tried to answer with irrelevant arguments. Then they denied that 
the experiments gave the results described by Newton, or main- 
tained that if the experiments were correct the conclusions drawn 
from them were false. Finally, it was alleged that if Newton's ideas 
were justifiable, they were not original. Neglecting the minor 
critics, it may be doubted whether either Hooke or Huygens 
two of the leaders of the scientific movement ever succeeded 
entirely in adjusting their thinking in accordance with the evidence 

1 Cambridge MS. Add. 3996: cf. the author's note in Cambridge Historical 
Journal, vol. IX (1948), pp. 239-50. 


of Newton's experiments. The former never understood that his 
own pulse-theory could not account for them. The latter, in his 
Traite de la Lumiere (1690), tactfully omitted the subject of colour 
completely. Their failure is not more surprising than that of other 
scientists in more recent periods who have equally resisted an 
innovation which has inevitably overwhelmed their criticism. 
Newton's propositions were revolutionary, not only in their con- 
tent, but because they were founded straightforwardly on new 
experimental evidence. It is, in one sense, an indication of the 
superficiality of the change in spirit effected by the scientific revo- 
lution that such obvious conclusions drawn from such easily 
repeatable experiments should have been treated as matters for 
argument. Empiricism that is, in this instance, Newton's reti- 
cence in his original papers on the question of what light is, and 
the reasons for the properties exhibited by a lens or prism was 
still obstructed by the inertia of established theory, which could 
prevent an accurate factual description being estimated at its true 
worth. In another sense, the dispute carried on in the pages of the 
Philosophical Transactions was the product of a confusion between 
facts and their interpretation which is perhaps inevitable in 
science at its growing point. Of this there are many examples, in 
the incredulity with which Lavoisier, Darwin, Joule or Pasteur 
was heard. Major scientific advances have not been made simply 
by uttering the statement that, in certain conditions, "The red 
line is higher than the blue," or " the thermometer reading was #." 
Newton did not make such a purely descriptive statement, for he 
added that the red was higher than the blue because the constituent 
coloured rays of white light are not equally refrangible. If un- 
comfortable experiments have stuck in the throats of those wedded 
to established ideas, it is owing to their indissoluble connection 
with a heterodox theory. In such circumstances, the new theo- 
retical attitude may seem to leave incomprehensible more than 
it seeks to explain, and then the question arises: "Is it worth 
while to alter the balance which is already struck between the 
mysteriousness of nature and human understanding?" 

The most important of Newton's discoveries, because they were 
most unconventional, aroused in many of his contemporaries the 
feeling that the accepted conception of natural processes was being 
wantonly disturbed in order to account for phenomena that 
could equally well be treated without such intellectual upheavals. 


It is, in the last resort, the function of cumulative experiment and 
observation to prove that such supposed alternatives in explana- 
tion are unreal; triumphantly to defend the old, or vindicate the 
new. In the course of the scientific revolution, the dominant 
antithesis had been between old and new methods and ideas, 
broadly divisions among the "moderns" were trivial. Towards the 
end of the seventeenth century this antithesis was becoming lifeless, 
and other divisions between the moderns themselves became far 
more critical. The appeal to experiment and observation had 
played a useful part in resolving the former antithesis, but the 
appeal to a new conception of what science should be, to a new 
image of nature, to a new mathematics and structure of reasoning, 
in short to a new appraisal of familiar facts, had achieved far 
more sweeping results. In many ways, genuine observation and 
experiment had been the pivots of seventeenth-century biology 
far more than they had been of its mechanics and physics. With 
the empiricist reaction against Cartesian science, which had 
seemed for a moment almost to sum up the whole revolt against 
tradition, and especially with the discoveries of Newton, came the 
test of the ability of the heirs of Copernicus and Galileo to resolve 
their own internal contradictions. If these were not in turn to lead 
to endless debate, such as had embroiled the heirs of Aristotle, it 
could only be by a more rigorous attention to the criteria of 
experiment. The fundamental significance of Newton's scientific 
method was that it achieved this exactly; it did not show merely 
that a theory roughly agreed with a selected group of facts, but 
that a group however limited and restricted of theoretical 
propositions could be associated with a range of experimental 
facts, carefully checked and often repeated. Confidence could be 
granted to such a group of propositions because it was unique, 
and the minimum necessary; because it claimed only to compre- 
hend a limited range of phenomena that had been exactly studied, 
and not to extrapolate from a few particulars to universal truths. 
Against such a method the kind of criticism directed towards 
Newton's theory of colour was unavailing in the long run; as was 
that directed against Lavoisier or Joule. If, with regard to Newton, 
expressions of incredulity were less well founded, it was perhaps 
because his precise use of the experimental method was not yet 

Of course Newton did not restrict himself entirely to such 



theoretical propositions as were firmly based on experiment. Too 
much has been made of his celebrated obiter dictum, " I do not frame 
hypotheses." Scattered through his works, and more freely through 
his unpublished papers, are numerous comments suggestive of a 
deeper penetration into the mysteriousness of nature than exact 
science could yet achieve. Newton framed many hypotheses 
which, he was inclined to think, might account for natural 
phenomena, like gravitation or refraction, hardly as yet illumi- 
nated by experimental inquiry; but he was always careful to 
distinguish between such hypotheses and an experimentally 
established theory. With him this distinction totally ignored by 
Descartes becomes fully self-conscious; hence the form of the 
Queries in the Opticks. In these Queries Newton sketched out an 
interlocking but not wholly consistent body of ideas relating to 
the nature of light and matter which he regarded as possible, or 
probable, but unproven. The most influential portions of this 
discussion were those in which Newton considered the relative 
merits of the undulatory (or pulse) and the corpuscular theories 
of light. He has been generally regarded, with some truth, as the 
classical advocate of the latter. But he was not wholly decided. 
For example, in Query 13 the suggestion is made that the colour 
of a ray depends upon the "bigness" of its vibration, the shortest 
vibrations corresponding to violet, and the largest to red, just as 
the pitch of sound corresponds to the " bigness" of the vibration 
in the medium. 1 Again, in Query 16, Newton asks, 'considering 
the lastingness of the Motions excited in the bottom of the Eye by 
Light, are they not of a vibrating nature?'; and in Query 17 he 
suggests that when a ray of light is reflected or refracted, vibrations 
are set up in the medium which, radiating from the point of 
incidence, c overtake the Rays of Light, and by overtaking them 
successively, do they not put them into the Fits of easy Reflexion 
and easy Transmission described above? ' As for the medium whose 
vibrations should transmit light, Newton could conceive of an 
aether, less dense than air but far more elastic, pervading all bodies 
and expanded throughout the universe, transmitting heat by its 
vibrations as well as light, 2 acting as the agent of reflection and 

1 Newton's terminology is obscure: it is not quite clear whether by " bigness " 
he means amplitude or wave-length. 

1 The existence of invisible (infra-red) heat rays was first demonstrated by 
Sir William Herschel (1800). 


refraction. Conversely, in Query 29 Newton declares: 'Are not 
the Rays of Light very small Bodies emitted from shining Sub- 
stances? For such Bodies will pass through uniform Mediums in 
right Lines without bending into the Shadow, which is the Nature 
of Rays of Light.' 

Colour might be accounted for by supposing that the smallest 
corpuscles of light gave the sensation violet, and the largest, being 
less refracted, the sensation red. From his study of the double 
refraction in Icelandic spar (which Huygens, in his Traiti de la 
Lumihe, had failed to explain completely in terms of the wave- 
theory) Newton concluded that the " sides" of a ray of light 
might have different properties, and he did not see how these 
could be associated with wave-propagation. These two points 
were, for him, decisive objections against the ideas of Hooke and 
Huygens, yet he himself found it necessary to conceive of a 
periodicity in the "Fits of Easy Reflection and Transmission" 
which he introduced in Book II in order to deal with the pheno- 
mena now ascribed to optical interference. 1 Newton's corpuscular 
theory, therefore, did not render an aether unnecessary, nor did it 
dispense entirely with the concept of aetherial vibrations. As he 
was evidently not satisfied with its completeness, it was unfortu- 
nate that some later physicists paid insufficient attention to 
Newton's caution: 'Since I have not finish'd this part of my 
Design, I shall conclude with proposing only some Queries, in 
order to a farther search to be made by others.' 

Not only does the Principia differ from the Opticks in form a 
mathematical, as compared with an experimental, treatise but 
its relationship to the contemporary scientific background is 
different also. It presented no less of a puzzle to contemporaries 
than the optical discoveries of fifteen years earlier, partly for the 
same reason that Newton chose to propound even apparently 
absurd theories if they alone suited the facts described, partly for 
the additional reason that the propositions of the Principia seemed 
to contravene the mechanistic philosophy which science had so 

1 In each regularly successive "Fit of Easy Reflection'* the ray tended to be 
reflected upon meeting a surface; in between in the " Fits of Easy Transmission " 
to penetrate into it. Thus the behaviour of a ray encountering the two surfaces 
of a thin medium (such as the air gap between two glass plates) depended 
upon the dimensions of the intervals between the surfaces and of the intervals 
between the "Fits." 


recently adopted with confidence. The theory of gravitation stated 
in terms of action at a distance was regarded by Cartesians as 
no better than a revival of the occult forces from which science 
had been liberated by mechanical hypotheses. Nevertheless, the 
Principia was far more in keeping with a certain scientific tradition 
one overshadowed by the triumph of Cartesian science than 
was the Opticks; its thesis was more clearly anticipated in earlier 
notions, due to Gilbert, Kepler, Borelli and Hooke; its materials 
had largely been prepared by other hands than those of Newton 

Descartes had flatly denied the validity of attraction as a 
scientific concept. Since all forces were mechanical in his view, a 
body could move only because other bodies impacted upon it, 
and so impelled it by pushing. Therefore he had described prob- 
able ways in which gravitational, magnetic, or electric "attrac- 
tions" might be caused by such impacts of the matiere subtile upon 
solid bodies. His system implied that the various motions of the 
planets around the sun were conditioned by the structure of 
the solar system as a whole, and particularly by the properties 
of the aetherial matter, rotating like a vortex, with which it was 
filled. They were not determined by separate relations between 
the individual celestial bodies; this perhaps explains why Kepler's 
empirical laws of planetary motion were of little interest to him. 
The earlier notions of attraction, however, had conceived rather 
of each celestial body, regarded as a physical entity, exerting an 
influence directly upon cognate matter. In Aristotle's theory of 
gravity and levity the matter of the universe was drawn, or 
attracted, to its natural place, the attraction being specific to 
each kind of matter, since earth could not tend naturally to the 
place of fire, nor vice versa. Thus the same kind of matter tended 
to collect together in the same place. In the Copernican system, 
this concept of attraction to specific spherical layers about the 
centre of the universe no longer had meaning, but the cosmic order 
could be preserved by transferring the attraction from the place 
to the matter which had, in Aristotle's cosmology, occupied that 
place. The basic principle that matter tends to coalesce with like 
matter implied by Aristotle, could now emerge more clearly. 
For Gilbert this principle, justified quite naively by theological 
reasoning, enabled bodies to preserve their integrity. 'Cohesion 
of parts, and aggregation of matter, exist in the Sun, in the Moon, 


in the planets, in the fixed stars,' so that in all these bodies the 
parts tend to unite with the whole 'with which they connect 
themselves with the same appetence as terrestrial things, which we 
call heavy, with the Earth.' 1 This means that gravitation is a 
universal property of matter, but peculiar to each body; the same 
gravity is not common to all, in Gilbert's view, because a piece of 
lunar matter would always tend towards the moon, and never 
adhere to the earth. 

It might seem that after Galileo's contention that the matter of 
earth, moon and planets the non-luminous heavenly bodies 
was of the same kind, it would have been a straightforward step 
to argue that all this earthy matter shared a common attraction, 
like drawing like. But against such an argument the teleological 
framework of the theory of attraction which was in no way 
required to explain the known behaviour of lunar or solar matter, 
apart from its consistency was doubly effective. In the first place, 
if the matter of the moon, for example, were attracted towards 
the earth, the theory would cease to explain the cohesion of the 
parts of the moon. Secondly, a common gravitational attraction 
would suggest that all the earthy matter in the universe would 
collect in one mass and this was Aristotle's view, which Galileo 
opposed. Thirdly, neither Galileo nor any of his contemporaries 
knew of any function which such a common attraction could be 
supposed to fulfil. The theory of specific attractions remained far 
more plausible. 

This theory had been used by Gilbert, and by Copernicus before 
him, as an alternative to the Aristotelean causation of the motions 
of heavy terrestrial bodies. It was less a new cosmological principle, 
than a new physical principle applied to cosmology. As such it is 
also used by Kepler: 

A mathematical point, whether it be the centre of the universe or not, 
cannot move heavy bodies either effectively or objectively so that 
they approach itself. ... It is impossible, that the form of a stone, 
moving its mass [corpus], should seek a mathematical point or the 
centre of the world, except with respect to the body in which that 
point resides. . . . Gravity is a mutual corporeal affection between 
cognate bodies towards their union or conjunction (of which kind the 
magnetic faculty is also), so that the Earth draws a stone much more 
than the stone seeks the Earth. Supposing the Earth to be in the 

1 On the Magnet, trans, by S. P. Thompson (London, 1900), pp. 219, 229. 


centre of the Universe, heavy bodies would not be borne to the 
centre of the Universe as such, but to the centre of a cognate spherical 
body, to wil the Earth. And thus wherever the Earth is assumed to be 
carried by its animal faculty, heavy bodies will always tend towards it. 1 

So far Kepler has said nothing very new. He has repeated that 
the concept of attraction of like to like can replace the Aristotelean 
concept of matter being attracted to specific places, and he has 
limited his use of this concept to heavy bodies cognate with the 
earth. But he has stated, for the first time, that the attraction 
is mutual (the analogy between gravity and magnetism, so fruit- 
fully begun by Gilbert, is now being extended), and this point he 
amplified further: 

If two stones were placed close together in any place in the Universe 
outside the sphere of the virtue of a third cognate body, they would 
like two magnetic bodies come together at an intermediate point, 
each moving such a distance towards the other, as the mass of the 
other is in proportion to its own. 

Here an original conception of the magnitude of the motion due 

to gravitational attraction was introduced ( --* = 2 ), in which it 

W 2 0*1 / 

was related to the ratio of the masses of the two bodies. Kepler, 
therefore, began the investiture of the theory of attraction with a 
definite dynamical form. Further, he postulated that the earth and 
the moon were cognate matter, like the two stones: 

If the Moon and the Earth were not retained, each in its orbit, by 
their animal or other equivalent forces, the Earth would ascend 
towards the Moon one fifty-fourth part of the distance between them, 
and the Moon descend towards the Earth about fifty- three parts; and 
they would there join together; assuming, however, that the substance 
of each is of one and the same density. 2 

Kepler then went on to demonstrate, from the ebbing and 
flowing of the tides, that this attractive force in the moon does 
actually extend to the earth, pulling the waters of the seas towards 
itself; much more likely was it that the far greater attractive force 
of the earth would reach to the moon, and greatly beyond it, so 
that no kind of earthy matter could escape from it. 3 

1 Astronomia Nova; Gesammelte Werke, vol. Ill, pp. 24-5. 

2 Assuming also that the diameter of the earth is about 3! (v/5s) that of the 
moon, which is a little too large. 

3 Loc. cit., pp. 25-7. 


Clearly no one invented the theory of gravitational attraction; 
it grew through many diverse stages. And clearly also the genesis 
of the theory of universal gravitation is found in Kepler. Newton's 
hasty calculation of 1666, his later theory of the moon, and his 
theory of the tides, are all embryonically sketched in the Astronomia 
Nova. But the attraction was still specific, applicable only to heavy, 
earthy matter; Kepler himself did not go so far as to suppose that 
the sun and planets were also mutually attracting masses, or that 
the dynamical balance he indicated as retaining the earth and 
moon in their orbits with respect to each other also preserved the 
stability of the planetary orbits with respect to the sun. He failed, 
as Copernicus, Gilbert and Galileo failed, to see the full power of 
gravitational attraction as a cosmological concept. 

Nevertheless, Kepler's idea that the satellite revolving round a 
central body is maintained in its path by two forces, one of which 
is an attraction towards the central body, although applied only to 
the earth-moon system, holds the key to all that followed and to 
the Principia itself. Galileo, like Copernicus, had believed the 
planetary revolutions to be "natural," i.e. inertial; the celestial 
bodies were subject to no forces. Kepler, however, believed that the 
motive force of the universe resided in the sun which, rotating 
upon its own axis, 'emits from itself through the extent of the 
Universe an immaterial image [species] of its body, analogous to 
the immaterial image [species] of its light, which image is itself 
rotated also like a most swift whirlpool and carries round with 
itself the bodies of the planets.' 1 Each planet, moreover, was en- 
dowed with its own "soul" which influenced its motions. 2 Such 
notions confused the dynamical elements of the situation for 
Kepler since the sun's force operated tangentially upon the 
planet, he did not imagine that a centripetal force was necessary 
to retain it in the orbit. In the singular case of the earth and moon, 
it was necessary for him to suppose that the "animal or other 
equivalent force" of the moon was sufficient to overcome the 
attraction towards the earth which would have distorted its path. 
This physical, attractive property of heavy matter could not as yet 
be made the basis of the stability of the celestial system; rather it 
was a disturbing feature which the cosmological properties of the 
heavenly bodies had to overcome. 

1 Loc. cit., p. 34. 

2 Cf. Harmonices Mundi (1619), Gesammelte Werke, vol. VI, p. 264 et seq. 


With Descartes the position was altogether reversed. He knew 
that bodies in free motion move in straight lines. He knew that his 
planets, swirled like Kepler's in a solar vortex, would if uncon- 
strained travel in straight lines outside its limits. He knew, there- 
fore, that some centripetal force must bend these straight lines 
into the closed curves of the orbits. Rejecting Kepler's mysterious 
attraction, he supposed this force to be provided by the varying 
density of the solar vortex, which resisted the planets' natural 
tendency to recede towards its periphery. 

After the publication of Descartes' Principia Philosophic ( 1 644) 
which for the first time applied the law of inertia systematically to 
the planetary motions, the elements of the problem of universal 
gravitation were completely assembled. The essential step was to 
replace Descartes' conception of the nature of the centripetal 
force required to hold the universe together by the Keplerian idea 
of attraction, with the sun taken as the central body. Kepler's 
problem could now be approached from a completely fresh aspect: 
knowing that the moon must be, as it were, chained to the earth 
to prevent it flying off into space, might not this bond be that 
"corporeal affection between cognate bodies towards their union" 
described by Kepler? Three men, all about the year 1665, formu- 
lated this question in similar terms, and attempted to answer it: 
Alphonso Borelli, Robert Hooke and Isaac Newton. 

Borelli, who was a member of the Accademia del Cimento, tried 
to find in Kepler's ideas the basis for a complete mathematico- 
mechanical system of the universe. 1 He regarded the light-rays 
radiating from the sun as levers pressing upon the planets, re- 
volving because the sun revolved, and able to exert a pressure 
because they were themselves material emanations. He explained 
that the least force would impart some motion to the greatest mass, 
and that therefore (in the absence of resistance) the planets would 
move with a speed proportionate to the force impressed. 2 This, 
like Kepler, he supposed to become more feeble as the distance 
from the sun was greater, so that the outer planets would move 
more slowly than the inner. Instructed by Descartes, Borelli knew 
that under such circumstances a centripetal force was necessary to 

1 Theories Mediceorum Planetarum ex cattsis physicis deduct* (Florence, 1666). 

2 As Prof. Koyr has pointed out, Borelli has unwittingly formulated the 
Aristotelean doctrine. Acceleration, not velocity, is proportional to force 
applied: hence Borelli's planets could never maintain a uniform speed. 


maintain the planets in their orbits, but he carefully avoided speak- 
ing of this as an attraction since the word was banned from the 
phraseology of mechanism. Nor did he identify this force with 
that which in the earth is called gravity. Instead, he postulated 
that all satellites in the celestial machine had a natural tendency 
or appetite to approach the central body about which they re- 
volve thus the planets sought the sun an appetite constant at 
all distances, and not at all affecting the central body itself. The 
stability of the planet in its orbit was therefore conditioned by the 
perfect balance of the centrifugal and centripetal forces to which 
it was subject, and this he was able to illustrate experimentally; 
but Borelli was further required to explain why these orbits are 
elliptical, not circular. The answer is highly ingenious: Borelli 
imagined that each planet was created outside its circular orbit. 
In this position the excess of centripetal over centrifugal force 
would urge the planet to its proper distance from the sun, but the 
momentum acquired would carry it beyond, to a point inside the 
circular orbit. Here the centrifugal would exceed the centripetal 
force, and the planet would again be pressed outwards, and again 
carried by momentum to its former station. l Then the cycle would 
be repeated. Thus the ellipse was a result of a slow oscillation 
about a stable position a circle round the central body com- 
pared by Borelli to the oscillation of a pendulum, to and fro, 
passing through a stable position at the perpendicular. This hypo- 
thesis was in accord with the observed fact that the velocity of the 
planet is greatest at its nearest approach to the sun. 

Borelli's theory, an amalgamation of those of Kepler and 
Descartes, in regarding the planets as impelled by a sort of vortex 
centred upon the sun conceived of the universe as a driven, not 
a free-spinning, machine. To it the law of inertia could not be 
directly applied hence Borelli's confusion concerning force and 
momentum. Both Hooke and Newton took two more important 
steps: they assumed that the planetary motions were purely in- 
ertial the universe was a great top and that there was a uni- 
versal, mutual attraction between masses of matter. Newton, 
moreover, remedying the mistakes in the principles of dynamics 

1 Nearly two hundred years later, Clerk-Maxwell accounted for the stability 
of the innumerable small satellites which compose Saturn's rings in a mathe- 
matical analysis, the principle of which was dimly anticipated in this hypothesis 
of Borelli. 


which permeate Borelli's treatise, effected a meticulous analysis 
of the forces which the latter (and Hooke) had described so 

There is ample evidence that by 1 685 Robert Hooke had a very 
complete picture of a mechanical system of the universe founded 
on universal gravitation. In the early days of the Royal Society he 
performed unsuccessful experiments to discover whether gravity 
varies above and below the earth's surface. In Micrographia (1665) 
he conjectured that the moon might have a 'gravitating prin- 
ciple' like the earth. In a discourse read to the Royal Society in 
1666 Hooke improved on Borelli with the supposition that a 
'direct motion' might be inflected into a curve by 'an attractive 
property of the body placed at the centre.' 1 Like earlier writers he 
compared this centripetal attraction to the tension in the string 
of a conical pendulum, which retains the bob in its circular path. 
In 1678 he wrote: 'I suppose the gravitating power of the Sun in 
the center of this part of the Heaven in which we are, hath an 
attractive power upon all the planets, . . . and that those again 
have a respect answerable.' 2 This is the first enunciation of the 
true theory of universal gravitation of gravity as a universal 
principle that binds all the bodies of the solar system together. 
The same force whereby the heavenly bodies 'attract their own 
parts, and keep them from flying from them,' also attracts 'all 
the other celestial bodies within the sphere of this activity.' It is 
this force which, in the sun, bends the rectilinear motions of the 
planets into closed curves. And this force is 'the more powerful in 
operating, by how much nearer the body wrought upon is' to the 
attracting body. 3 

These ideas, Hooke claimed, he had expounded as early as 
1670. But it was not until 1679 that he hit upon a hypothesis to 
describe the rate at which the gravitational attraction should de- 
crease with distance. In that year he renewed his correspondence 
with Newton, discussing an experiment to detect the earth's rota- 
tion through the deviation of falling bodies. This in turn led to a 
debate on the nature of the curve which a heavy body would 
describe if it were supposed to be able to fall freely towards the 
centre of the earth, during which (in a letter to Newton dated 

1 R. T. Gunther: Early Science in Oxford, vol. VI (Oxford, 1930), p. 266. 

2 Ibid., vol. VIII, p. 228. 

3 Ibid., vol. VIII, pp. 27-8, 229-30, etc. 


6 January 1 680) Hooke stated the proposition that the force of 
gravity is inversely proportional to the square of the distance, 
measured from the centre of the gravitating mass. 1 He was con- 
vinced that this "inverse square law" of attraction, combined 
with the ideas he had already sketched out, would be sufficient to 
explain all the planetary motions. 

Hooke's scientific intuition was certainly brilliant. Of all the 
early Fellows of the Royal Society, in a generation richly endowed 
with genius, his was the mind most spontaneously, and sanely, 
imaginative; schemes for new experiments and observations oc- 
curred to him so readily that each day was divided between a 
multiplicity of investigations; physiology, microscopy, astronomy, 
chemistry, mechanics, optics, were each in rapid succession sub- 
jects for his insight and ingenuity. No topic could ever be broached 
without Hooke rising to make a number of pertinent points and 
to suggest fruitful methods of inquiry. With regard to celestial 
mechanics, Hooke's conception was as far-reaching as Newton's; 
but it was not prior and it was not proven. The publication of the 
Principia, accompanied by Hooke's charge of plagiary against 
Newton, inflamed the suspicion between the two men into out- 
raged anger. Both suffered from a touchy pride; neither would 
recognize the true merits of the other. In Newton's eyes, Hooke 
grasped after other men's achievements, having merely patched 
together some notions borrowed from Kepler, Borelli and Huy- 
gens. To Hooke, Newton had merely turned into mathematical 
symbols ideas that he had himself already expressed without at- 
tracting notice or reward. He was ever unwilling to admit the 
supreme advantage that Newton held over himself, of being 
mathematician enough to demonstrate as a theory, confirmed by 
observation, that which Hooke himself had only been able to 
assert as a hypothesis. In fact the different status which attaches 
to a scientific theory and a scientific hypothesis a difference which 

1 Hooke thought that this same law would apply to the force of gravity 
below the earth's surface. Newton later proved (Principia, Bk. I, Prop. LXXIII) 
that within a sphere the centripetal force is inversely proportional to the dis- 
tance from the centre, not to the square of the distance. Ismael Bouillau, in 
Astronomia Philolaica (1645), had argued that the intensity of Kepler's "moving 

virtue" resident in the sun would decrease, like that of light, as ^. Therefore, 

he said, since the velocities of the planets are not in this proportion to their 
distances from the sun, they could not be impelled by such a force emanating 
from it. 


Newton emphasized more than once was something to which 
Hooke proved himself insensitive by a number of episodes in his 
career. As Newton pointed out, Hooke did not invent the theory 
of attractive forces, as such; and after Huy gens' theorems on the 
centrifugal acceleration of rotating masses had been published, 
the inverse square law could easily be deduced. Granting the 
highest merit to Hooke's scientific intuition, it is quite clear from 
certain confusions inherent in the development of his hypothesis 
between 1666 and 1685 that his mastery of the principles of 
dynamics was never completely confident, and that his thought 
was never safeguarded by the precision of mathematical analysis. 
Newton complained, in a letter to Halley at the time when 
Hooke was voicing his protests before the Royal Society, that the 
latter wished to assign to him the status of a mathematical drudge 
and claim for himself the sole invention of a new system of celestial 
mechanics. The truth is far otherwise. By 1666 Newton was al- 
ready able to calculate centrifugal accelerations. This calculation, 
applied to Kepler's laws, gave him the inverse square law of 
attraction. 1 If the earth's gravitational attraction was assumed to 
act upon the moon, he computed that in accordance with this law, 
at the distance of the moon from the earth this centripetal force 
would be " pretty nearly" equal to the centrifugal force created 
by the moon's own revolution about the earth. Gravity would be 
precisely the chain required to bind the moon in its orbit. 2 But 
such a calculation was not strictly appropriate: for a planet's 
(and the moon's) orbit is not circular but elliptical, with the central 
body (sun or earth) at one focus of the ellipse. Moreover, in calcu- 
lating the distances and relative forces, Newton had proceeded as 
though the earth and moon were points, that is, reckoned that if 


the force of gravity at the surface of the earth was , then at the 

1 In a circle of radius r, if T is the time taken by a body to complete one 
revolution, the centripetal force required to hold it in its path is F -=3. But 
according to Kepler's Third Law, in the solar system T 2 = k'r*. Substituting, 
F = ^/-g whence, omitting the constants, F is proportional to -^. 

2 Newton's calculation in 1666 did not give a perfect confirmation of the 
inverse square law, because the value he took for the earth's radius (and hence 
the distance of the moon from the earth) was too small. It used to be 'supposed 
that this discrepancy induced him to lay the matter aside. The view given below 
is now generally accepted. 



moon it was ;~ y 2 . He had not proved that the external gravita- 
tional attraction of a sphere could be computed as though its mass 
were concentrated in a point at the centre. The difficulties in- 
volved in perfecting the hypothesis upon which his first casual 
trial was founded were mainly mathematical, and at this time 
beyond Newton's skill. So great were they that Halley was aston- 
ished to learn (in 1684) that Newton had overcome them; had 
proved, in fact, that the path followed by a body, moving obliquely 
in relation to a second which exerts a centripetal force upon it, 
must correspond to one of the conic sections. 1 

In 1666, therefore, Newton was not satisfied that the inverse 
square law represented more than an approximation to the truth. 
Impressed by the mathematical difficulties involved, he laid the 
hypothesis aside. For about thirteen years (1666-79) there is not 
the least evidence that he paid any attention to dynamics, uni- 
versal gravitation or celestial mechanics. Optics, mathematics, 
alchemy and perhaps already theology, filled his mind. So much, 
at least, Newton owed to Hooke: that he was compelled to return 
to his former hypothesis. Even when driven, by Hooke's unwel- 
come letters, to review the mystery of gravity, he was guilty of 
blunders and misapprehensions. Even when, pricked by Hooke's 
corrections, he had solved the problem of the inverse square law 
and the elliptical orbit, Newton once more set his success to cool 
for a further five years. Only Halley's visit to Cambridge in 1684, 
and the warmth of his admiration and offers of assistance, set the 
Principia in train. 

The book is often described as though its sole function was to 
establish what has been called the Newtonian system of the uni- 
verse. That it did so is, indeed, its main historical importance; the 
Third Book and the System of the World, in which Newton set him- 
self directly to this task, are likely to be read with far greater 
interest than the earlier sections. But Newton's influence on subse- 
quent science, in this work alone, penetrated to a far greater 
depth. He defined mass and the laws of motion. He gave to science 
formal concepts of space and time which needed no revision for 

1 Newton established (Principia, Bk. Ill, Prop. XL) that the path of a comet 
is a parabola, and that the orbit of a returning cornet, such as that examined 
by Halley (ibid., Prop. XLI), is an extended ellipse of which the portion near 
the sun is scarcely distinguishable from a parabola. 


two centuries. He expounded and exemplified a " method of 
philosophizing" that is still regarded as a valid model. He virtually 
created theoretical physics as a mathematical science in the form 
which it preserved to the end of the last century. For Newton, the 
mathematical principles in nature were not merely evidenced by 
the elementary dynamics of Galileo, or even by his own majestic 
computations relating to the planetary motions, but were to be 
traced in the whole field of experimental physics and more 
conjecturally in the phenomena of light, in the constitution of 
matter and the operations of chemistry. Outside physics, Newton's 
work was never finished it could not be finished and his ideas 
remained half-formed. The Principia, however, is a treatise on 
physics almost as much as it is a treatise on celestial mechanics; 
and in some sections Newton made meticulous use of the quantita- 
tive experimental method. 1 The theorems and experiments on the 
vibrations of pendulums in resisting media, on the free fall of 
bodies and the trajectory of projectiles in the same, are not perhaps 
of great intrinsic interest, as certainly they were of no practical 
importance, nor closely relevant to the motions of the planets; but 
it is not impossible to understand why Newton concerned himself 
with them. For, firstly, such problems were close to the heart of 
seventeenth-century physics, in a tradition which Newton himself 
brought to a climax. And secondly, they served to prove his point 
that the principles of nature are mathematical; that with number 
and measure science could reach beyond the uncontrolled imagina- 
tion of a Descartes, or even the idealism of a Galileo. In Newton's 
eyes, scientific comprehension was not limited to vague qualitative 
theories on the one hand, or definite statements about a state of 
affairs much simpler than that which is actually experienced on 
the other; it could proceed, by due techniques, to definite ideas 
about all that is physical, down to the properties of each constituent 
corpuscle. To illustrate this conception of science is the purpose of 
the Principia. 

Otherwise, both logically and emotionally, the framework of 
celestial mechanics would have been without foundation. Here 
Newton and Descartes were more alike than the crude antithesis 
of their cosmologies would allow. Descartes had proceeded, in the 
Principles of Philosophy, from his clear ideas of what must be, 

3 Thus, fresh experiments on the descent of heavy bodies in resisting media 
were added by him to each of the later editions of 1713 and 1726. 


through the laws of motion and the properties of moving bodies, 
to his celestial mechanism. Newton likewise: developing his 
mathematical method from the definitions and the laws of 
motion, through the long analyses of the motions of bodies in many 
different circumstances until he could discern in the heavenly 
motions special cases of those principles of motion that he had 
already elucidated. Newton perceived, as Descartes had done, as 
Huygens did when he all but abandoned Descartes, that a theory 
which attributed the most noble and enduring phenomena in 
nature to the play of mechanical forces could not stand on a 
handful of assumptions, two or three happy computations and the 
vague, undemonstrative, mechanistic philosophy that had become 
fashionable. 1 Like Descartes, but with an infinitely more subtle 
logic, with all the rigour of mathematics and with cautious appeal 
to observation and experiment, Newton displayed the whole 
science of matter-in-motion before he turned to the solar system 
specifically. An unfinished treatise, De Motu Corporum, preceded 
the Principia; the study of a particle in motion must precede that 
of a circling planet. And if Newton found it necessary to investi- 
gate the solid of least resistance, or the flow of liquids, it was to 
prove the universality of that science of moving particles that he 
proposed to apply, not to a minute part, but to the whole of man's 
physical environment. The Principia, in fact, does not expound a 
particular scientific theory to account for the motions of the 
heavens, it develops a theory of physical nature which embraces 
these phenomena, and all phenomena of matter-in-motion, within 
its compass. 

As such it was, of course, a mechanistic theory. No other was, 
or is, conceivable within the range of physics. Not that Newton 
excluded God from the universe: 

This most beautiful system of the sun, planets, and comets, could only 
proceed from the counsel and dominion of an intelligent and power- 
ful Being. ... He endures forever, and is everywhere present; and 
by existing always and everywhere, he constitutes duration and 
space. 2 

1 In this, of couise, Newton powerfully revealed his immense superiority 
over Hooke, who could never have constructed the laborious scaffolding upon 
which Book III of the Principia is raised. 

2 General Scholium, concluding the Principia. Gf. Florian Gajori: Sir Isaac 
Newton* s Mathematical Principles of Natural Philosophy (Berkeley, 1946), pp. 544-6. 


God was for Newton the Final Cause of things, but, excellent and 
laborious theologian as he was, he made no confusion between 
physics and theology. 1 That Newton seemed, by the theory of 
universal gravitation, to contravene the principles of mechanism, 
was due to misapprehension. Though certain phrases in the Prin- 
cipia might seem to indicate the contrary, he did not believe 
that gravity was an innate property of matter, nor that two 
masses could attract each other at a distance without having any 
mechanical relationship. To Bentley Newton wrote: 

It is inconceivable that inanimate brute matter should, without the 
mediation of something else, which is not material, operate upon and 
affect other matter without mutual contact. . . . That gravity 
should be innate, inherent, and essential to matter, so that one body 
may act upon another at a distance through a vacuum, without the 
mediation of anything else, by and through which their action and 
force may be conveyed from one to another, is to me so great an 
absurdity that I believe no man who has in philosophical matters a 
competent faculty of thinking, can ever fall into it. 2 

He added to the second edition of the Principia a brief statement 
that by attraction he meant only to describe the tendency of bodies 
to approach each other, no matter what the cause. As to the prob- 
able nature of this cause, he professed himself ignorant. 3 It was 
sufficient to infer that the phenomenon existed and was universal; 
like Galileo, Newton regarded the effect as established if it could 
be described, though the cause were hidden. To suppose that par- 
ticles or masses exert a gravitational attraction was not, therefore, 
in Newton's language to postulate an occult quality in matter but 
to describe a fact a fact that was to be demonstrated in the 
laboratory by Henry Cavendish seventy years after Newton's 
death. Nor did Newton believe that the celestial spaces across 
which the sun's attraction holds the planets in their orbits were 
necessarily empty of all matter. 

His refusal to ascribe a cause or mechanism to universal gravi- 
tation was indeed one of Newton's principal advantages in celes- 

1 Newton, however, expressed a sentiment typical of the age in a letter to 
Bentley (1692): 'When I wrote my treatise about our system, I had an eye on 
such principles as might work with considering men for the belief of a Deity; 
and nothing can rejoice me more than to find it useful for that purpose.' (Ibid., 

P. 66 9 ). 

2 Quoted by Cajori, op. cit. 9 p. 634. 

3 In a letter to Boyle, he outlined a theory of aetherial contraction which he 
never troubled to develop thoroughly. 


tial mechanics. He was free, as the Cartesians were not, simply to 
state and analyse the observable facts, and the inferences neces- 
sarily drawn from them. He did not seek to construct a model 
which would be rendered clumsy and contradictory by the 
very attempt to explain everything in nature by corpuscular 

Hypotheses [wrote Newton], whether metaphysical or physical, 
whether of occult qualities or mechanical, have no place in experi- 
mental philosophy. . . . l And to us it is enough that gravity does 
really exist, and act according to laws which we have explained, and 
abundantly serves to account for all the motions of the celestial 
bodies, and of our sea. 2 

The concluding paragraph of this General Scholium indicated a 
possible solution of many "occult" mysteries, fully in the 
seventeenth-century mechanical tradition. For, 

We might add something concerning a most subtle spirit which per- 
vades and lies hid in all gross bodies; by the force and action of which 
spirit the particles of bodies attract one another at near distances, and 
cohere, if contiguous; and electric bodies operate to greater dis- 
tances . . .; and light is emitted, reflected, inflected, and heats 
bodies; and all sensation is excited, and the members of animal bodies 
move at the command of the will. . . . 

Newton's imagination was not less generous than that of Descartes, 
though less dogmatic. He was as fully convinced of the existence 
of an (Bther^ the residuum of the major secrets of nature, as Descartes 
or any nineteenth-century physicist. Further hints were to be given 
years later in the Queries appended to the Opticks, but Newton did 
not know how these things could be investigated, much less proved. 
Nevertheless, his attitude (less plain certainly in the first edition 
of the Principle than it has since become) was widely misunder- 
stood. Newtonian empiricism was rapidly accepted by his own 
countrymen: probably no scientist has received a more immediate, 
or a warmer, acclaim from the intellectuals as well as the professed 
scientists of his race. Abroad it was distrusted. Neither Huygens 
nor Leibniz (who set the tone for many lesser men) could stomach 

1 Newton, of course, did not mean that tentative hypotheses have no use in 
an investigation; he framed many such himself. He meant that an unconfirmed 
and undemonstrated hypothesis should not be taught as an adequate theory. 

2 Gajori, op. cit., p. 547. 



the downright statement of Proposition VII, Book III. 1 Attempts 
to reconcile the Cartesian mechanical theory of celestial vortices 
with Newtonian mathematical laws were prolonged into the mid- 
eighteenth century. Not until fifty years after the publication of 
the Principia did Voltaire's proclamation of his admiration for the 
profound English geniuses, Newton and Locke, begin to win ad- 
herents. The essential truth, that Newton and Descartes shared 
the same idea of nature, was thus long obscured; and Newton has 
perhaps been too often praised for being other than he was. The 
idol of perfection who was endowed by the nineteenth century 
with every attribute of scientific insight and vigour, with abhor- 
rence of hypothesis and mystery, with serene temper and con- 
ventional religion, was not the genuine Newton. It is perhaps 
paradoxical but not unjust that his greatest successor was to 
arise not from the crowd of reverend English gentlemen who were 
to claim Newton as their own, but in the person of the sceptical 
French mathematician, the Marquis de Laplace, whose Mfoanique 
Celeste (1799-1825) extended in time the laws that Newton had 
traced in space. 

1 'That there is a power of gravity pertaining to all bodies, proportional to 
the several quantities of matter which they contain.* 


BEOLOGIGAL study, as it is practised today in laboratories and 
field stations, is essentially a creation of the nineteenth 
century. The work of Darwin on evolution, of Mendel on 
genetics, of Schleiden and others on the cell theory, so transformed 
the texture of the biologist's thought that it would be appropriate 
to attribute to the period 1830-70, rather than to any earlier age, 
the "biological revolution" which completed the modern scien- 
tific outlook. The belief in the fixity of species was no less respect- 
able than the belief in the fixity of the earth; the belief that the 
Creator must have personally attended to the fabrication of every 
kind of diatom and bramble was no less primitively animistic than 
the belief that His angels governed the revolutions of the planetary 
orbs. Exactly as the mechanistic philosophy of the seventeenth 
century was accused of encouraging scepticism and irreligion, on 
a greater scale (because the issue was more clear and more 
decisive) the mechanistic biologists of the nineteenth met the full 
force of ecclesiastical wrath. The liberty of the scientist to direct 
his theories in accordance with the scientific evidence alone was 
equally at stake. But there is this difference. Biology was certainly 
"modern" in some respects if not all before the nineteenth 
century. A great renaissance had already occurred, which itself 
far surpassed all that had gone before. Materials had been heaped 
up from which a great generalization such as evolution could be 
drawn. Above all, the scientific method of biology was already in 
existence that was not the creation of the nineteenth century. 
The researches of Leeuwenhoek and Malpighi, the systematics of 
Ray and Linnaeus, were preliminaries as essential to the syntheses 
which introduced the truly modern outlook as the work of 
Copernicus and Galileo was to that of Newton. 

None of the ancient founders of biology was primarily in- 
terested in collection, description and classification as ends in 
themselves. Aristotle the zoologist and Theophrastus the botanist 
were always philosophers their purpose was to investigate the 



functioning of living organisms; Dioscorides studied botany as the 
servant of medicine. Partly, perhaps, because the range of species 
examined was comparatively small neither Aristotle nor Theo- 
phrastus knew more than about five hundred distinct kinds of 
animals or plants the problem of cataloguing them did not 
become of overriding importance, though much thought was given 
to order and arrangement. Since the Greek empire extended into 
India, exotic species were available, but they did not attract 
great attention. 1 To the Greek mind, the attempt to answer the 
questions that living nature posed was more important than the 
compilation of information, and for this the materials close at 
hand were sufficient. Over-leaping a great space of time, in the 
last century collection and taxonomy have again become no more 
than specialized branches of biology. The study of function, of 
the processes of growth and differentiation, has assumed a more 
fundamental importance. The experimental has replaced the 
encyclopaedic method, so that a modern zoologist may find a 
greater interest in the works of Aristotle than in those of any 
natural historian of the pre-Darwinian age. 

The intervening period has, indeed, very special characteristics. 
For long there were no adequate successors to the Greek botanists 
of the fourth century B.C. The Romans were competent writers on 
agriculture, but such an author as Pliny added nothing beyond 
the cult of marvels to the existing texts which he pillaged. The 
philosophic spirit of the Greeks almost perished, and was only 
revived in the botanical work of Albert the Great (De Vegetabilibus 
et Plantis, c. 1250). Albert was an Aristotelean botanist at least, 
his main authority was a translation of two books on plants then 
attributed to Aristotle. 2 He was interested in the philosophy of 
plant growth, in the variety of their structures and (as he believed) 
in their constant mutations. Care in the morphological analysis 
of plants for purposes of description and identification was com- 
bined with renewed attention to the problem of classification, but 
Albert was not greatly impressed by the importance of cata- 
loguing. Such an emphasis was then unusual, for in his time 
herbalism medical botany had already become a principal 
interest. It is a strange paradox that while the learning of the 

1 One important exception was the date-palm, which provided the only 
example of sexuality in plants known before the late seventeenth century. 

2 But now assigned to Nicholas of Damascus (first century B.C.). 


later middle ages turned so naturally to argument in metaphysics 
and philosophy, and thence to logic, cosmology and physics, the 
intellectual problems posed by the living state were so often 
ignored. Only in its relations with medicine can medieval biology 
be generally said to have had a serious intellectual content, to 
have attempted to answer questions. 

Herbalism looked to Dioscorides, rather than to Aristotle and 
Theophrastus. Before the fall of Rome the tradition he founded 
had already suffered debasement and the decline, both in matter 
and in illustration, continued throughout the early middle ages. 
In the thirteenth century, however, there were already skilful 
herbalists with a good knowledge of Dioscorides and his com- 
mentators, some familiarity with exotic drugs, and an interest in 
description and identification. The herbal of one of them, Rufinus, 
serves to show that he, at least, did not scruple to add remarks 
of his own to the literary tradition, and that he was aware of 
distinctions in kind unknown to the more famous compilers of 
the sixteenth century. 1 Rufinus was clearly well acquainted with 
drug plants and druggists, but he made no attempt to classify, 
merely arranging his notes in alphabetical order. The greater part 
of his text was made up of quotations from earlier pharmacological 
authorities (Dioscorides, the Circa instans of about 1 1 50, the Tables 
of Salerno, and others), but Rufinus' own additions were mostly 
botanical, such as this description of Aaron's Beard: 

Aaron's Beard has leaves which are thick in substance, nearly a span 
broad and long, and it has two little beards to each leaf. The leaves 
are divided down to the root. It has a tuberous root in the ground, 
from which a cosmetic ointment is made, and it sometimes has 
blotched leaves. It forms its flower in a capsule, contrived by a 
marvellous artifice and having this yellowish capsule around it, in 
the centre of which is a sort of finger, with two little "apples" below 
it, wonderfully contrived. The plant which has blotched leaves is 
masculine and that without blotches on the leaves is feminine. 2 

His manuscript was apparently unillustrated, so that the identifi- 
cation of uncommon plants from it would have been very doubtful. 
The herbal flourished, to become enormously popular soon 
after the invention of printing. But the herbalist's interest in the 
plant was always in knowledge of means to an end. Some of his 

1 Lynn Thorndike: The Herbal of Rufinus (Chicago, 1946). 

ibid., P . 54. 


medicaments were minerals, or derived from animal sources, and 
it was only because such a large proportion of medieval physic 
was derived from vegetables, that the pharmacopoeia assumed a 
preponderantly botanical form. Thus descriptive zoology was a 
poor relation of herbalism, though animals were also described 
as the immediate companions and servants of man, because they 
offered useful moral lessons, and because some of them had an 
exotic or symbolic fascination. Conceiving that the world was 
created for the use and instruction of man in working out his 
own salvation, the medieval mind naturally adopted a somewhat 
functional approach to the living state. The task of the naturalist 
was simply to describe living things, with their particular uses (or 
wonders, or edifying properties) so that other men might use them 
(or wonder at them, or be edified). Despite the occasional philo- 
sophic questioning of an Albert, there was no powerful motive to 
elevate him above a lexicographical mentality. And the naturalist 
was less interested in collecting facts about creatures that might 
form the material of a science, than in human reactions to this 
and that, in the diseases against which a given plant was supposed 
to be beneficial, in the moral to be drawn from the habits of the 

Thus the origins of natural history were essentially anthropo- 
centric, in the Roman Pliny, in the early Christian compilers like 
Isidore of Seville, in the thirteenth-century encyclopaedia of 
Bartholomew the Englishman, in the late medieval herbalists. 
Human interest in nature was limited to the production of a 
catalogue raisonnt. 

The early stages of the renaissance brought no important re- 
orientation. Occasionally the representational art of a " Gothic" 
stone mason or wood carver had enriched a cathedral with a 
recognizable likeness of a living species. About the beginning of 
the fifteenth century the graphic artist began to realize the 
aesthetic possibilities of exact imitation of nature in the illumination 
of manuscripts here were the roots of both the naturalistic art 
of a Diirer, and biological illustration. By 1550 the technique of 
life-like illustration had been mastered, with greatest distinction 
in the herbals of Brunfels (1530) and Fuchs (1542). This technique 
was ultimately as necessary to botany and zoology as. to human 
anatomy, but it did not occasion any immediate enhancement of 
the level of botanical knowledge, for the texts of both Brunfels' 


and Fuchs' books were poor, and excelled in description by 
unillustrated works, such as that of Valerius Cordus. Brunfels, 
indeed, tried to find some more natural arrangement than that 
of an alphabetical list, but the latter was by no means abandoned 
as yet. The botanists of the sixteenth century, with the exception 
of Cesalpino and Gesner, were still herbalists, and the herbal was 
still an adjunct to the pharmacopoeia, enabling the apothecary to 
identify such medicinal plants as Swallow-wort and Fennel, Sage 
and Fumitory, whose names are perpetuated on the delightful 
majolica drug-pots of the time. 

Humanism had its effect upon biology, as upon all branches of 
science, without challenging the main emphasis on collection and 
classification. The authority of Dioscorides and Theophrastus was 
reinforced rather than weakened; their texts were better under- 
stood, but did not encourage originality in ideas. Mediterranean 
botanists particularly took up the task of identifying more exactly 
the species described by Dioscorides; some, like Mattiolo, Cordus 
and Conrad Gesner, were content to put forward their own work 
as expansions of his, with considerable display of philological 
learning. Gradually it was learnt that Greek names had been 
abused by application to species quite different from those known 
to the Greeks themselves; and that, moreover, the name often 
covered a whole group of similar plants, not a specific type. 
Northern botanists, on the other hand, acquired knowledge of 
plants not included in the traditional Mediterranean flora; Charles 
de 1'Ecluse alone is reputed to have found two hundred new 
species in Spain and Portugal (1576), and later he was equally 
successful in Austria and Hungary. Cataloguing and description 
were extended far beyond the range of the merely useful. Decora- 
tive plants, like the daffodil and horse-chestnut this last one of 
many importations into western Europe at this period were 
noticed as well as the medicinal, along with many new species 
reported by the explorers to the Far East and the Americas. The 
common and uncommon plants of hedgerow, pasture and upland 
were no longer neglected. A garden was now judged by the 
multitude, rarity and beauty of the species represented in it, while 
the Hortus Siccus became a repository of trophies exchanged among 
collectors. For the men of the renaissance collected plants, 
plumages and skins as they amassed coins, antique statuary and 
manuscripts, since greater wealth and leisure permitted such 


costly and learned ostentations. The plants in some renaissance 
gardens, like that of the Venetian patrician Michieli (c. 1565), 
were commemorated in water-colour and written description. 

Though the character of the product of this vastly increased 
activity in botany, or herbalism, was not greatly changed in the 
sixteenth century, the character of the new herbalist was certainly 
modified. As he attached less importance to medicinal value, he 
became more keenly interested in fine distinctions; whereas the 
ancient and medieval herbalist had hardly been concerned with a 
unit smaller than the genus, their successors began to discriminate 
between different species within the genera, and even between 
varieties of the same species. Again, the new naturalists were often 
scholars and gentlemen, they had therefore greater opportunities 
for botanizing over wide areas, even despatching emissaries for 
this purpose; they could acquire a more extensive literary know- 
ledge and employ the best draughtsmen. Doubtless such men felt 
the aesthetic appeal of nature more keenly than the apothecary or 
peasant. As Fuchs wrote: 

There is no reason why I should expatiate on the pleasure and delight 
of acquiring knowledge of plants, since there is no one who does not 
know that there is nothing in this life more pleasant and delightful 
than to wander over mountains, woods and fields garlanded and 
adorned with most exquisite little flowers and plants of various sorts. 
. . . But it increases that pleasure and delight not a little, if there be 
added an acquaintance with the virtues and powers of these plants. 1 

Fuchs' observation ends with a touch of that pedantry which has 
always divided the scientist from the artist; the scientific tendency 
is, after all, to dissect and destroy the thing of beauty, but there is 
no reason to doubt that the intellectual inquisitiveness which leads 
via microscope and herbarium to the unreadability of a Flora, may 
have its aesthetic foundation. This also links naturally with the 
urge to collect and preserve, the emphasis upon the rare and the 
expensive, which are so typical of biology from the sixteenth to 
the nineteenth century. Collector's mania has often been derided, 
yet it may yield genuine scholarship, as in (for example) the study 
of ceramics or bibliography. The botanist's character was more 
complex. He could claim that his activities were useful to man, 
and contributed to the worship of God. If Sir Joseph Banks' 

1 De Historia Stirpiwn (Basel, 1542), Preface, sig. aav. Quoted by A. Arber: 
Herbals (Cambridge, 1953), p. 67. 


attempts to transplant the breadfruit to the West Indies were 
vain, naturalists had great success with tobacco, the potato, maize 
and innumerable ornamental species. In nature they saw abund- 
ant evidence of Design, and so created the tradition which led 
through Ray's Wisdom of God to Paley's Natural Theology, or 
Evidence of the Existence and Attributes of the Deity , collected from the 
Appearances of Nature. There was thus a variety of arguments for 
commending biology to the attention of a serious and devout 
mind, of which medical utility was not the least important. Few 
naturalists in this period would have given whole-hearted support 
to the views of the Bohemian, Adam Zaluzian (1592): 

It is customary to connect Medicine with Botany, yet scientific treat- 
ment demands that we should consider each separately. For the fact 
is that in every art, theory must be disconnected and separated from 
practice, and the two must be dealt with singly and individually in 
their proper order before they are united. And for that reason, in 
order that Botany, which is (as it were) a special branch of Natural 
Philosophy, may form a unit by itself before it can be brought into 
connection with other sciences, it must be divided and unyoked 
from Medicine. 1 

The task of the descriptive biologist was also far more complex 
than that of the cataloguer of human artifacts, indeed, it was this 
complexity which enforced the development of systematics. Prob- 
lems of nomenclature, identification and classification rather 
suddenly became acute between 1550 and 1650, and constituted 
one of the main theoretical topics in biology for nearly three 
hundred years. Naturalists tried to follow a "natural" order of 
groupings which meant that they were long deceived by superficial 
characteristics. Aristotle had distinguished, in zoology, between 
viviparous and oviparous creatures, between the cephalopodia and 
other molluscs; Dioscorides had distributed plants among the four 
rough groups of trees, shrubs, bushes and herbs. Lesser distinc- 
tions, between eggs-with-shells and eggs-without-shells, between 
deciduous and non-deciduous, flowering and non-flowering, were 
also very ancient. In the main such distinctions were preserved as 
the basis of arrangement until late in the seventeenth century. 
Nomenclature was equally in need of reform, if standardization 
was to be obtained, and the name to have a logical connection 
with the system. Description was the very basis of a communion 
1 Methodi Herbaria Libri Tres, quoted in Arber, op. cit., p. 144. 


of understanding in biology, for on it depended the hope of arriv- 
ing at a single comprehensive Flora which would enable all men 
to agree upon the identity of any given specimen. Here the classical 
tradition was very frail, partly owing to the defects of its language 
in referring to the parts of animals and flowers. 

No consistent answers to the problems of taxonomy were pro- 
duced before the eighteenth century; even today the concept 
"species" cannot be exactly defined, and many systems of classifi- 
cation have succeeded that of Linnaeus. Nevertheless, the great 
compilers of the sixteenth century, in their attempts to make an 
encyclopaedic survey of all living things, more than mastered 
their Greek inheritance and demonstrated the fruits of exact ob- 
servation. Their view of their undertaking was of course far from 
strictly biological. Thus Conrad Gesner, in his enormous Historic 
Animalium (published 1551-1621), besides naming and describing 
the animal, discussed its natural functions, the quality of its soul, 
its use to man in general and as food or medicine in particular, and 
gave a'concordance of literary references to it. The Italian natural- 
ist Ulissi Aldrovandi strove for even deeper omniscience when (for 
example) writing of the Lion he noted at length its significance in 
dreams, its appearance in symbolism and mythology, and its use 
in hunting and tortures. But Aldrovandi was also one of the first 
zoologists to give a skeletal representation of his subjects where 
possible. Along with the spirit of sheer compilation there developed 
a growing tendency to specialize, exemplified in Rondelet's book 
on Fishes (1554), in Aldrovandi's treatise on the different breeds 
of dog, in the Englishman Thomas Moufet's Theatre of Insects 
(I634J. 1 All these works, and some portions of the vast encyclo- 
paedias, were written with conspicuous attention to the kind of 
detail that could only be obtained through systematic personal 
observation. Most of the old fables debasing natural history the 
birth of bees from the flesh of a dead calf, and of geese from 
barnacles, the inability of the elephant to bend its legs, and the 
tearfulness of crocodiles were at least doubted, though they 
lingered long in popular books. 

The classification of animals in accordance with Aristotle's 
scheme presented no great difficulties. The Latin names gave 
sufficient identification, superficial distinctions were marked. In the 

1 This, written about forty years earlier, was largely the work of Thomas 
Penny (c. 1530-88). 


group of oviparous quadrupeds, for instance, Gesner had only a 
few divisions frogs, lizards, tortoises and he knew only three or 
four different kinds in each. Plants were more recalcitrant. Alpha- 
betical lists had their uses, and so had others in which the groups 
consisted of plants having a similar habitat or function. When the 
attempt was made to render identification easier by adopting 
arrangements based on form and structure, more profound diffi- 
culties were encountered. In general, it seemed desirable to make 
the arrangement as natural as possible, by taking into considera- 
tion the maximum number of characteristics, but it was difficult 
to decide what the most important of these were. Reliance on 
superficial features, like the possession of prickles, or habits like 
climbing, was apt to prove very deceptive. The early systematists 
consequently tended to make increasing use of a single character- 
istic of the plant as a determinant de 1'Obel chose the leaf, and 
Cesalpino the seed. One advantage of this method was that it led 
to the more intensive study of particular parts of the plant, espe- 
cially the flower, and to the improvement of descriptive termi- 
nology. Such systems, of which Linnaeus' was the logical and 
highly successful climax, were artificial, convenient indices to the 
prodigality of nature; but they did promote conscious study of 
the problems of taxonomy. Before 1550 there were hardly any 
firm principles by which species were distinguished, while the 
arrangement of the species was a matter for the discretion of 
each author. By 1650 there was a great measure of agreement on 
specific identities, and it was gradually becoming clear that 
there was a difference between a search for a method, which would 
make identification easy, and an endeavour to trace the natural 
affinities between species and larger groupings. 

Attention to systematics was partly enforced by the sheer multi- 
plicity of species. Some six thousand distinct plants had already 
been described by 1600, and the number trebled during the follow- 
ing century. Since it was the pride of the good botanist to be able to 
identify every plant presented to him, or if it were a new species to 
indicate its relationship to known ones, there were strong reasons 
for correlating identification and arrangement with one or more 
morphological characteristics. Caspar Bauhin, in 1623, outlined 
the natural groupings of botanical species more clearly than any 
of his predecessors, and made more extensive use of the binomial 
nomenclature in which one element of the name was shared by the 


genus, or group of closely related species. A little later Jung, at 
Hamburg, greatly improved the technical description of the dis- 
position and shape of leaves, and of the various parts of the flower. 
A younger contemporary, the Englishman John Ray (1627-1705), 
laid the foundations of modern descriptive and systematic biology, 
in botany at least owing something to Jung's methods. Ray had 
some experience of dissection, but he was not an experimenter, nor 
a microscopist. Though his interests extended to the ecology, life- 
history and physiology of his subjects thus he was much more 
than a plain cataloguer he did not himself do much to advance 
the newer branches of biology growing up in his time. On the 
other hand, his philosophic and general scientific outlook was 
wider than that of most succeeding naturalists; like many other 
Fellows of the Royal Society, he was fascinated by technological 
progress, accepted the broad picture of a mechanistic universe 
under divine surveillance, and joined in the expulsion from biology 
of myth and mystery. 

Ray was perhaps the first biologist to write separate treatises on 
the principles of taxonomy. 1 These were exemplified in his great 
series of descriptive volumes, the Historia generalis plantamm (1686- 
1704) and Historia insectorum (1710), with the Ornithologia (1676) 
and Historia Piscium (1686) in which he collaborated with his 
patron, Francis Willughby. Taken together for all these books 
were actually written and published by Ray they represented 
by far the most complete and best arranged survey of living nature 
that had ever been attempted. Ray had exercised his keen faculty 
for observation intensively over the whole of England, and ex- 
tensively over much of western Europe; he was deeply learned in 
the writings of ancient and modern naturalists; above all, he wel- 
comed new ideas. From Grew he accepted as probable the sexual 
reproduction of plants; from Redi and Malpighi the experimental 
disproof of spontaneous generation; and he himself taught that 
fossils were the true remains of extinct species, not mere "sports" 
of nature nor God-implanted tests of man's faith in the truth of the 
Genesis story. If the enumeration of species was his principal task 
which still left him room for his Collection of English Proverbs, 
Topographical Observations, and Wisdom of God Ray was very far 
from supposing that classification was the end of biology.. 

In botanical systematics Ray favoured a "method" which was 

1 Methodus plantarum nova (1682); Synopsis methodica animalium quadrupedum et 
serpentini generis (1693); Methodus insectorum (1704). 


more natural than those of his contemporary Tournefort and his 
successor Linnaeus. He admitted that the familiar triple distinc- 
tion between trees, shrubs and herbs was popular rather than 
scientific, though he continued to use it while also making the far 
more fundamental distinction between mono- and dicotyledonous 
plants. For finer discrimination he relied upon no single character- 
istic but appealed to the forms of root, leaf, flower and fruit. The 
necessity for a formal method of classification was fully apparent 
to him it was particularly required by beginners in botany 


o tJ I Large 

r! ?* ,~ ^ 

S3 fe 

(Polypi, Crustacea) 

Jj ' (Insects) 

'With Lungs 

Without Lungs 

^ (Fishes) 

One ventricle 


(Oviparous quadrupeds, 

Two ventricle 
, Heart 

\ [Mammals] 

f Cetaceans 

With hoofs etc. 

With nails etc. 
Fig. 10. Ray's Classification of Animals 

but he did not expect that all living forms could be perfectly ac- 
commodated within it. Taxonomists would always have difficulty 
with 'species of doubtful classification linking one type with an- 
other and having something in common with both.' 1 In zoological 
classification Ray was perhaps even more successful, through 
basing his groups upon decisive anatomical features. He was the 
first taxonomist to make full use of the findings of comparative 
anatomy, particularly among mammals 2 and with regard to such 
characteristic features as feet and teeth, thereby discerning such 
groups as the Ungulates, Rodents, Ruminants, etc. (Fig. 10). This 
part of his work was freely adopted by Linnaeus. 

1 Cf. the Preface to Methodus Plantarum, and C. E. Raven: John Ray t Naturalist 
(Cambridge, 1950), Ch. viii. 

2 This class was recognized by Ray, though not given this name. 


Meanwhile, the naturalist's range of observation was being 
vastly extended by the microscope (Chapter 8). In the use of this 
instrument the primary emphasis was still on description; at this 
stage, attempts to construct elaborate theories upon the new evi- 
dence were infrequent and misleading. There was opportunity for 
the ramification of activity, and it was not neglected. The study 
of plant anatomy, originally enforced by the need for classificatory 
systems, could now proceed to the structure of tissues and repro- 
ductive mechanisms; zoological anatomy, likewise, stimulated by 
the fertility of the comparative method as shown by Harvey and 
many before him, was extended to strange creatures like the "orang- 
outang 55 (dissected by Dr Edward Tyson), 1 and, with the aid of the 
microscope, to levels of detail inaccessible to the naked eye. 

Most of this new work prolonged existing tendencies. Marcello 
Malpighi (1628-94), for example, completed Harvey 5 s discovery 
of the circulation of the blood by following its passage from the 
arterial to the venous system through the capillary vessels, at the 
same time observing its red corpuscles. He was also able to go 
farther than Harvey and Fabricius in examining the microscopic 
foetus of the chick within the first hours of incubation, from which 
he was led to believe that growth was a process of enlargement or 
unfolding only: the foetus was "pre-formed" in the unfertilized 
egg. 2 As a pioneer of histology Malpighi entered on less familiar 
ground, in his microscopic examinations of the liver, the kidney, 
the cortex of the brain, and the tongue, whose " taste buds 5 ' he 
discovered. In the study of insects where Aristotle had shown 
wonderful insight the serious scientific curiosity in which Mal- 
pighi was joined by Jan Swammerdam (1637-80) had already 
been anticipated by Hooke in Micrographia, and by even earlier 
virtuosi with their " flea-glasses." These two naturalists, however, 
were the first to explore fully the internal anatomy of minute 
creatures, demonstrating that their organs are as highly differenti- 
ated as those of large animals. Malpighi's treatise on the silkworm 
has been described as the earliest monograph on an invertebrate; 
in it he indicated the function of the trachea first observed by him, 
which distribute air about the insect's body, and of other tubes by 

1 Cf. M. F. A. Montagu, Edward Tyson, M.D., F.R.S. 1650-1708 (Memoir 
XX, Amer. Phil. Soc., Philadelphia, 1943). The creature was, in fact a 
chimpanzee. Tyson also published monographs on the "porpess", rattlesnake, 
opossum etc. 

2 Joseph Needham: History of Embryology (Cambridge, 1934), pp. 144 etseq. 


which the products of metabolism are excreted. He did much 
work on the anatomy of the larval stages of insects, and observed 
their evolution to maturity, but here he was excelled by Swammer- 
dam, who also denied that there was any true transformation, even 
in the emergence of the butterfly from the caterpillar, or of the 
frog from the tadpole processes which he studied with enormous 
care. In sheer technical skill exemplified in the quality of his 
drawings as well as in the fineness of his dissection under the lens 
and his unique methods of injection Swammerdam foreshadowed 
the greater manipulative resources of the mid-nineteenth century. 
Leeuwenhoek is chiefly remarkable for his work at much higher 
magnifications and the discovery of a new world inhabited by 
Infusoria and Bacteria (p. 241), but the ubiquitous curiosity which 
led him to examine hairs, nerves, the bile, parts of plants, crystals 
indeed almost everything that could be brought before his 
lenses induced him to make some observations comparable to 
those of Malpighi and Swammerdam, among which those on the 
compound insect eye and on ants were particularly novel. From 
observations on aphids he discovered parthenogenesis in animals 
reproduction by the female parent alone. 

In the plant kingdom, the microscope could not reveal a new 
order of magnitude within the living state, as it did in the animal; 
on the other hand, a much clearer idea of the structure of plant 
tissues emerged including the description of their minute com- 
ponents, the cells than was yet obtained in zoology. The pre- 
sumed anatomical and physiological analogies between animals 
and plants were indeed powerful incentives to inquiry at this 
time. Sometimes analogy was wholly misleading, as with the 
theory (popular until disproved by repeated experiments) that 
the sap in plants circulates like the blood in animals, but in other 
aspects, as when the " breathing" of plants was compared with 
that of animals by Malpighi and later by Stephen Hales (1679- 
1761), it led towards a more correct understanding. Malpighi, 
despite the excellence of his descriptions of the differing structures 
found in wood, pith, leaf and flower under the microscope, and 
of the germination of seedlings, thought too exclusively in terms 
of the animal form. Thus he wrongly identified the function of the 
spiral vessels that he observed in plant tissue with that of the 
tracheae in insects, and erected upon this identification a broad 
theory of the increasing specialization of the respiratory organs, 


reaching its climax in mammals. He also tried to find in plants 
the reproductive organs familiar from vertebrate anatomy. The 
Englishman, Nehemiah Grew (1641-1712), whose independent 
work is closely parallel to that of Malpighi, and of equal quality, 
was a more restrained observer, though he believed (as he quaintly 
wrote) 'that a Plant is, as it were, an Animal in Quires, as an Animal 
is a Plant, or rather several Plants, bound up into one volume ' a 
remark which, however strange the metaphor, expresses profound 

Grew was well aware, not only that the aims of ordinary natural- 
ists still fell far short of attainment, but that these aims by no 
means amounted to a true "Knowledge of Nature." His Philosophical 
History of Plants (iSjz) 1 sketched a new and far more ambitious 
programme. Many of the problems he proposed remain unsolved: 

First, by what means it is that a Plant, or any Part of it, comes to 
Grow , a Seed to put forth a Root and Trunk. . . . How the Aliment 
by which a Plant is fed, is duly prepared in its several Parts. . . . How 
not only their Sizes, but also their Shapes are so exceeding various. . . . 
Then to inquire, What should be the reason of their various Motions; 
that the Root should descend; that its descent should sometimes be 
perpendicular, sometimes more level: That the Trunk doth ascend, and 
that the ascent thereof, as to the space of Time wherein it is made, is 
of different measures. . . . Further, what may be the Causes as of 
the Seasons of their Growth; so of the Periods of their Lives; some being 
Annual, others Biennial, others Perennial . . . and lastly in what 
manner the Seed is prepared, formed and fitted for Propagation. 

Some of these questions Grew himself tried to elucidate, most 
brilliantly deducing that plants reproduce sexually, the flowers 
being hermaphrodite like snails, with the stamens acting as the 
male organs. 2 Nor did he neglect the possibility of examining the 
plant substance by combustion, calcination, distillation and other 
experimental methods of chemistry, though these were as yet too 
primitive to be of real service. In this way he showed that the 
matter of the pithy or starchy part of the plant was quite distinct 
from that of the woody or fibrous part. Like Ray and other 
naturalists Grew saw no reason to reject mechanism as a working 

1 Reprinted in The Anatomy of Plants (London, 1682). 

2 Op. cit., pp. 171-3. Hermaphroditism is not, of course, universal among 
plants, as Grew thought. 


hypothesis which he developed (for example) in his account of 
plant nutrition; as he put it, with a familiar simile: 

[We need not think] that there is any Contradiction, when Philosophy 
teaches that to be done by Mature:, which Religion, and the Sacred 
Scriptures, teach us to be done by God: no more, than to say, That 
the Ballance of a Watch is moved by the next Wheel, is to deny that 
Wheel, and the rest, to be moved by the Spring ; and that both the 
Spring, and all the other Parts, are caused to move together by the 
Maker of them. So God may be truly the Cause of This Effect, although 
a Thousand other Causes should be supposed to intervene: For all 
Nature is as one Great Engine, made by, and held in His Hand. 1 

A general sketch of the horizon in biology about the year 1 680 
would show virile activity, a steady expansion of the sphere of 
interest, and the fruitful exploitation of new techniques. Ad- 
mittedly Man was still the prime focus of attention, whether in 
the Royal Society's endeavour to introduce a scientific spirit into 
agriculture, or in the relics of the belief (still held by a plant- 
anatomist like Grew) that all vegetables have "virtues," or in 
the frequent backward glances of the zoologist at the human 
body. Nevertheless, as the peripheries rapidly became more remote 
they assumed, as it were, a territorial autonomy. The survival of 
anthropocentricity in the feverish concentration of Swammerdam 
was small. It is significant that naturalists no longer defended 
their preoccupations as useful, but rather as contributions to 
knowledge of the universe, of the organic part of the divinely 
created machine. And, though description and cataloguing of 
macroscopic flora and fauna remained their principal tasks, 
natural history showed clear signs of entering into partnerships 
in which the skills of the human anatomist and physiologist, 
the chemist, and the physicist, should be placed at its service. 
Gradually, through the seventeenth century, biology had returned 
to the philosophic attitude of an Aristotle; now it seemed likely 
that the borrowing of modern knowledge and techniques would 
permit the ancients to be as greatly excelled in these sciences as 
in physics and mechanics. 

Briefly, there was promise a promise of growth in depth and 
extent that was hardly fulfilled during the next century and a 
half. That it was not fulfilled may be attributed partly to the 

1 Op. tit., p. 80. 



fallaciousness of the early hopes, for neither microscopic technique, 
nor chemical experiment, were capable of changing the pattern 
of activity so permanently as the work done during the two 
decades 1660-80 would suggest. These crude tools were soon 
blunted. The close connection between biology and medicine, 
which had encouraged study of the former science in the seven- 
teenth century, tended to hamper its later development, for as 
medical studies were permeated by the influence of Galen's ideas 
until the nineteenth century, it was impossible that animal and 
plant studies should escape the limitations of those ideas. Unable, 
as yet, to build freely upwards upon the half-finished foundations 
of their predecessors, eighteenth-century naturalists might well 
be discouraged by the splendour of their inheritance. Discourage- 
ment was all the more harsh because this inheritance included 
such a feeble element of hypothesis to serve as a scaffolding for 
their own researches. Thereafter it is not surprising that they felt 
strongly a positive attraction that was both old and new. Like the 
sixteenth-century encyclopaedists, they were subjected to a vast 
incursus of new species, fruit of a renewed urge towards explora- 
tion that drove Linnaeus into the sub-arctic tundra, and Joseph 
Banks to the Pacific and Australasia. Moreover, this invasion 
synchronized, not with a sense of confusion before the profligacy 
of nature, but with an increasingly dogmatic confidence in a 
System, the system of Linnaeus. Quite suddenly, about the middle 
of the century, classification became one of the easiest, instead of 
one of the most difficult, biological exercises. Not for the first or 
the last time in science there was a rush to gather the harvest, 
while the unbroken fields were neglected. 

Admittedly, there was no very abrupt transition. In the early 
part of the century Leeuwenhoek was still active, and a little later 
Reaumur, one of the most versatile experimentalists of any age, 
began to publish his monumental Memoir es pour servir d Vhistoire des 
Insectes (1737-48) which continued the work of Malpighi and 
Swammerdam. Low-power microscopy was applied to aquatic 
subjects by Trembley, who experimented upon the capability 
for regeneration and asexual reproduction by budding that he 
discovered in fresh- water " polyps" (Hydra and Plumatella) , x and 
by Ellis (Natural History of the Corallines, 1755). Plant physiology 

1 Mtmoires pour servir d Vhistoire d'un genre de polypes d'eau douce ( 1 744) ; cf. 
J. R. Baker: Abraham Trembley of Geneva (London, 1952). 


was studied by Hales with the aid of quantitative physical methods 
largely derived from Boyle (Vegetable Staticks, 1727). He measured 
the upward pressure of the sap in the roots of plants, the quantity 
of water absorbed by the root and transpired by the leaves, and 
the rate of growth in different structures. He proved that some 
atmospheric substance entered into the composition of plants. 
Such experiments he tried to elucidate mechanically by others on 
the capillary attraction of water in fine tubes and porous sub- 
stances; somewhat similar ones were extended to the circulation 
of the blood in his Htemostaticks. Further important contributions 
to physiology were made by the contemporary chemist-physicians 
G. E. Stahl, Friedrich Hoffman and Hermann Bocrhaave, who 
also continued a seventeenth-century tradition. 

The physiological processes involved in reproduction and the 
formation of the embryo, in particular, remained a matter for 
heated controversy, on much the same lines as in the seventeenth 
century. In J. T. Ncedham spontaneous generation had a new 
champion, who found microscopic animalculae in boiled broth 
that was (as he thought) effectively sealed from the air (1748). He 
was answered in more precise experiments by Spallanzani (1767), 
but this question was not regarded as decisively settled up to the 
time of Pasteur. The great debate between Ovists and Animal- 
culists was more widespread, and even less fruitful. Harvey had 
believed in epigenesis, that is, that the growth of the embryo 
proceeded both by the gradual differentiation of its parts, and by 
their increase in size: 'there is no part of the foetus actually in 
[the egg], yet all the parts of it are in [the egg] potentially.' The 
effect of microscopy, soon after Harvey's death, was to give 
immediate advantage to the alternative theory of preformation, 
according to which the embryo merely swelled from being an 
invisible speck which was from the first completely differentiated; 
as Henry Power said: ' So admirable is every organ of this machine 
of ours formed, that every part within us is intirely made, when the 
whole organ seems too little to have any parts at all.' Preformation 
was developed especially by Malpighi and Swammerdam. Since 
the embryo, among oviparous creatures, develops in the maternal 
egg, and microscopists believed that the first signs of its future 
form could be detected as soon as the egg appeared, it was natur- 
ally assumed by them that the embryo, or potential embryo, was 
solely derived from the female. This view conveniently opposed 


the unfashionable Aristotelean conception that the male, supplying 
the active "form," was the prime agent in generation, and 
the female responsible merely for the passive "substance" of the 
offspring. Aristotle seemed to be further confounded by the 
discovery of the mammalian ovum attributed to De Graaf (1672). 
This supposed discovery was premature De Graaf saw the 
follicles since known by his name, and the true ovum was first 
described by von Baer a century and a half later. However, it 
brought about an essentially correct change of thought, to the 
view that both viviparous and oviparous reproduction begin with 
the fertilization of an egg formed in the female. According to 
the Ovists, the ovum contained the embryo not potentially but 
actually, and in the version of their theory known as emboitement 
they supposed that this held within its own organs the ova of the 
next generation, and so on ad infinitum like a series of Chinese 
boxes: in the ovaries of Eve were confined the future forms of all 
the human race. 

The discovery of spermatozoa opened up a contrasting but 
parallel theory. Leeuwenhoek, in one of his rare flights of hypo- 
thesis, suggested that these "little animals" were the living 
embryos, which were enabled to grow by transplantation into the 
egg: c If your Harvey and our De Graaf had seen the hundredth 
part they would have stated, as I did, that it is exclusively the 
male semen that forms the foetus, and that all that the woman 
may contribute only serves to receive the semen and feed it.' 1 He 
supported this doctrine by reference to well-known cases where 
the offspring was strongly marked with the characteristics of the 
male parent. Hartsoeker (1694) and Plantades (1699) the last 
perhaps as a deliberate fraud published illustrations of a 
"homunculus" enclosed in the head of a spermatozoon. Emboite- 
ment was also taken up by the Animalculists in the eighteenth 
century. Rival interpretations of observations that were commonly 
very imperfect and carelessly recorded continued for over a 
hundred years. Some regarded the spermatozoa as products of 
corruption, like the eel-worms in vinegar, for it was only in 1824 
that they were proved essential to fertilization by Dumas and 
Provost; at about the same time the experiments of Geoffroy 
Saint-Hilaire on the production of monsters proved that the 

1 Letter to Nehemiah Grew, 18 March 1678. Collected Letters, vol. II, 
(Amsterdam, 1941), p. 335. 


appearance of the embryo is not preformed or predestined. At an 
earlier date the scientist-mystic Swedenborg favoured epigenesis 
(c. 1740), and more powerful support came from the researches 
of Caspar Wolff at St. Petersburg (1768), who pointed out that, 
as in plants the rudiments of flowers develop from undifferentiated 
tissues and are at first undistinguishable from those of leaves, so in 
animals no miniature foetus could be found in the earliest phase 
of development, after which the nervous system, the blood-vessels, 
and the alimentary canal were observed to arise in successive 
stages. Generally speaking, however, the reaction against pre- 
formation (and the consequent expiry of the Ovist-Animalculist 
controversy) did not occur until the close of the eighteenth century, 
although, as F. J. Cole has said, the admirable iconography of 
Malpighi carried its own refutation of its author's doctrines. 1 

In most other branches of biology the eighteenth century 
appears equally unproductive of truly creative investigation. In 
its more medical aspects, such as human and comparative 
anatomy, and human physiology, the successes of the seventeenth 
century were extended, particularly during the last two decades. 
Lavoisier, for example, was able as a result of his new theory of 
combustion to throw fresh light on animal respiration. But the 
greatest biological achievement of the period, that which won the 
greatest fame and attracted the greatest number of pupils, was 
certainly that of Carl Linnaeus (1707-78). His mastery of the 
order of nature 'God,' as he complacently acknowledged, 'had 
suffered him to peep into His secret cabinet ' touched the imagi- 
nation of a generation already turning towards a romantic 
naturalism, which was soon to cherish Gilbert White and Thomas 
Bewick, to prefer landscapes to portraiture, and to talk contentedly 
of the noble savage. Linnaeus was the prophet of Wordsworth. 
His arrogance, like Samuel Johnson's, enslaved admiration, while 
the confidence with which he wrote as though personally present 
at the Creation was the more acceptable (in that, in all respects, 
it reassured the somewhat conventional religious conscience of the 
age) because it counteracted the scientific agnosticism of Voltaire 
and the French pkilosophes. Most of the major advances of science 
have, in one way or another, imperilled the comfortable security 
of the popular understanding. One great merit of Linnaeus' in- 
tellect was that, save in his great gift for classification, it was 
1 F. J. Cole: Early Theories of Sexual Generation (Oxford, 1930), p. 147. 


remarkably undistinguished; he had neither the wish nor the 
power to e* pater les bourgeois. 

That does not detract from the importance of his work. Linnaeus 
was a sincere amateur of nature in all her moods; a competent 
teacher of many subjects in biology and medicine, able to inspire 
affection and devotion in his students; a voluminous and lucid 
writer. Like Newton, he possessed a strong, though not wholly 
attractive, character. Like Newton too, he saw the essentials of a 
problem and solved it. And he was only slightly less dominant 
than Newton in forcing future naturalists to follow the path that 
he had cleared. 

The Linnean systems of classification embraced the animal, vege- 
table and mineral kingdoms, and even diseases. Of these the 
second was by far the most complex, and the most influential. It 
was derived by applying to the immense descriptive materials 
amassed by Ray, Tournefort and others of his predecessors the 
principle of plant sexuality firmly demonstrated by the experiments 
of Camerarius (1694). Thus plants were distributed into twenty- 
four Classes according to the number, proportions or situations of 
the stamens (male organs), and each Class further subdivided in 
accordance with the number of styles (female organs) . The first 
three Classes in this system were Monandria (i stamen), Diandria 
(2 stamens), and Triandria; the Class Polyadelphia had "stamens 
united by their filaments into three or more sets." In each Class 
plants with one style were assigned to an Order named Mono- 
gynia, those with two to the Order Digynia, those with three to 
the Order Trigynia, etc. Each Order, easily determinable by in- 
spection of the flower, contained a number of genera, which 
groups Linnaeus regarded as primary and as "naturally" distinct. 
Each genus had a brief description of the features common to all 
the species included in it, mainly derived again from the method 
of fructification. In further division into species the shape of the 
leaves and other characteristics became important. For example, 
Genus 696 in Linnaeus' System of Mature is found in the Class Hex- 
andria, Order Monogynia; it is called Berberis, and is distinguished 
by "Calyx 6-leaved, petals 6, with two glands at the base of each, 
style o, berry superior, 2-seeded." In this genus Linnaeus reported 
five species, one European, one Cretan, one Siberian, and two 
from Tierra del Fuego. 

The main principles of this classification apparently became 


clear to Linnaeus at an early age, and were worked out with the 
aid of the experience gained in the course of his journey through 
Lapland ( 1 732) and during later European travel. The first version 
of the System of Nature (1735) was written in Holland when he was 
acting as botanical curator to Boerhaave. The illustrations of the 
principles were extended vastly in the subsequent editions which 
speedily issued from the press. (The tenth, of 1758, is now the 
standard work of reference.) The utility of the work depended 
very much upon the rigidly methodical, and extremely succinct, 
descriptions, which in turn were made possible by the use of a 
technical terminology that was largely of Linnaeus' own creation. 
He also paid great attention to nomenclature: 

As I turn ovei the laborious works of the authorities, I observe them 
busied all day long with discovering plants, describing them, draw- 
ing them, bringing them under genera and classes: I find, however, 
among them few philosophers, and hardly any who have attempted 
to develop nomenclature, one of the two foundations of Botany, 
though that a name should remain unshaken is quite as essential as 
attention to genera. 1 

The rules which Linnaeus drew up for coping with this problem 
anticipated in part those now accepted by international agree- 
ment, and within a few years his binomial system was universally 
accepted among naturalists. 

The Linnean Order was determined by a purely mechanical 
procedure. To it might be assigned thousands of different plants. 
How were the further distinctions to be defined, and the lines 
drawn between mere differences of variety, those of species, and 
those of genus? Even post-Linnean taxonomy has not succeeded 
in drawing such lines firmly, and in practice Linnaeus made much 
use of earlier experience. The concept of species is indeed some- 
thing that can easily be grasped intuitively Aristotle had it in 
perfect clarity for in very primitive languages the kinds of ani- 
mals and plants are named even though the general concept 
"plant" or "animal" is lacking. In surveying kinds of creatures, 
it is not difficult to see why dog, wolf and hyena are more like each 
other than any member of another group containing lion, tiger 
and panther. The difficulty arises as the analysis of what consti- 
tutes an effective likeness or unlikeness has to be made finer and 

1 Critica Botanica, translated by Sir Arthur Hort, Ray Society (London, 1938) ; 


finer: should the wolf (which is interfertile with the dog) be placed 
in the same genus with the pekinese? Linnaeus realized that though 
the species is the fundamental unit of taxonomy, the assignment 
of the generic boundaries is the classifier's most tricky task. Here 
he could offer no rigid rules, though he stated certain negative 
propositions, and therefore his success was empirical rather than 
theoretical. His system could be made to work, but because generic 
groupings depended upon one man's notion of significant simili- 
tude, it was far from infallible. 

Although unable to define the characteristics of a species and a 
genus precisely, Linnaeus did associate ideas with each of these 
concepts that were received as dogmatic truths up to the time of 
Darwin. Some had long been current without winning universal 
credence. The most important of them was the fixity of species, 
which Ray had not admitted. In Linnaeus' view each species 
represented the descendants of an original entity, or pair of enti- 
ties, individually created at the beginning of the world. Its flora 
and fauna had always been exactly as they are now, and hence 
the concept of species was justified (if not, in practice, defined) by 
common descent from a unique created form, just as humanity 
was defined by common descent from Adam. Equally, the disap- 
pearance of species was ruled out, despite the evidence of fossils, 
which were thus denied an organic origin. 1 

Until late in life Linnaeus regarded the production of fertile, 
stable hybrids by crossings between members of the same genus as 
impossible; intergeneric hybrids were unthinkable. Shortly before 
1 760 new evidence led Linnaeus to believe that new species could 
arise have arisen through differentiation by crossing. Perhaps 
after all only the ancestors of the Orders were created but he 
never perfected this thought, of which he seemed ashamed, and 
though he withdrew from subsequent editions of the System of 
Nature confident statements that new species never occur, the 
recantation came too late. It is strange that the chief legacy of 
Linnean biology, the main scientific argument against Darwin, was 
a doctrine in which the mature Linnaeus had himself lost faith. 2 

1 Linnaeus was more orthodox than Steno, Hooke, Ray and others who 
admitted that living species represented only by fossilized shells, teeth or bone 
had disappeared from the world, incompatible as this seemed with divine 
Providence, and the care taken to preserve all the land-anima'ls at the time of 
the Flood. 

2 Gf. Knut Hagberg: Carl Linrueus (London, 1952), Chapter XII. 


It is important to recollect that there was already, before the 
end of the century, significant opposition to the doctrine of the 
immutability of species. Evolutionary ideas were first applied to 
the formation of the earth's crust, not its peopling with creatures. 
Descartes and Leibniz, Burnet and Whiston, had each before 1 700 
devised an hypothesis to account for the separating out of rock and 
water from an incandescent mass or primitive chaos, and traced 
the depression of ocean-beds, the elevation of mountain ranges, to 
the action throughout long periods of purely mechanical forces, 
though the time-scale imagined was absurdly short. The first two 
of these ignored the story of the Flood completely. Fossils, if ac- 
cepted as organic remains, enforced the conclusion that species 
had either changed, or disappeared. The great French naturalist, 
Georges Cuvier (1769-1832), who founded the science of palaeon- 
tology, favoured the second hypothesis. Successive catastrophes 
of which the Biblical Flood was the most recent had swept the 
earth of life; successive creations had re-peopled it with new 
species. His influence, more than any other, reinforced that of 
Linnaeus in deriding evolutionary ideas, and in creating the in- 
tolerant assurance in immutability which faced Darwin. But his 
compatriot Buffon (1707-88), a man of less pretentious scientific 
authority, whose main effort was directed towards descriptive 
biology in the forty-four volumes of his Histoire Naturelle (once im- 
mensely popular, now a dead weight in booksellers' basements) 
chose the alternative explanation. For Buffon, as for Aristotle and 
Ray, the living process became more complex by infinitesimal 
gradations: 'Le polype d'eau douce sera, si Ton veut, le dernier 
des animaux et la premiere des plantes.' The power to reproduce 
in kind, and to grow, he regarded as the prime characteristic of 
the living state. This power resided in "organic molecules," the 
basic units of both plants and animals; death was the dispersion 
of these molecules, nourishment their assimilation into the body 
of the creature. Denying preformation in all its aspects, Buffon 
asserted that the segregation of the " organic molecules" in the 
sexual organs was the cause of reproduction, just as, in a different 
way, it caused the generation of parasites. The organic molecules 
had been the same since the beginning of the world; but, as he 
stressed in his fipoques de la Nature, the world itself had altered, 
evolved. In the Fifth Epoch elephants had roamed the far north; 
the earth was hotter in its youth, and of greater vitality. Animals 


were larger, witness the ammonites big as cartwheels, the huge 
tusks found in Siberia, perhaps even man was then a giant. In 
general, Buffon imagined that the change in nature was towards 
degeneration, but he was acute enough to see that where human 
purposefulness had intervened, species had been changed for the 
better. Bread-wheat, for example, was not a gift of nature, for it is 
unknown in the wild state; it is evidently a herb brought to per- 
fection by man's care and industry. ' Our best fruits and nuts ' he 
wrote, ' which are so different from those formerly cultivated, that 
they have no resemblance save in the name, must likewise be re- 
ferred to a very modern date.' By selective breeding, man has in 
a manner created secondary species which he can multiply at 
pleasure.' Although, in such passages, Buffon seems to tread upon 
the heels of Darwin, and although the fixity of species (together 
with the taxonomical nicety attached to that doctrine) was alien 
to his mind, he made no great play with the idea of evolution. It 
was not, for him, an explanatory concept. He did not make it his 
task to account for the origin of specific differences. 

Thus, in a variety of ways, the elements of modern biology grew 
out of the older natural history. Their growth was necessarily 
spasmodic since it was not autogenous, the stages of the trans- 
formation of the naturalist into the biologist being fixed by the 
availability of techniques and ideas borrowed from physics, chem- 
istry, medicine and philosophy. In the sixteenth century natural 
history became a respectable branch of study; in the eighteenth it 
was moulded into a formal discipline by Linnaeus; but the special 
quality of the seventeenth century, which made biologists of men 
like Harvey, Descartes, Hooke, Redi and Leeuwenhoek, who were 
not naturalists, was the rich opportunity for opening up new sub- 
jects, largely with the aid of imported methods. That the physical 
science, and general intellectual climate, of the eighteenth century 
had less in comparison to offer to the biologist was the chief reason 
for the failure of these new subjects to continue their startling 
initial progress. 

The distinction between natural history and biology is not, of 
course, recent. Aristotle was a naturalist in the History of Animals, 
a biologist in the Generation of Animals. In the scientific renaissance, 
the writings of such an embryologist as Fabricius clearly fall into 
a different category from those of Gesner. But the distinction is 


one which the events of the nineteenth century finally made plain. 
Through this perspective, a man who studies the courtship of 
birds is certainly a naturalist; another who examines the differ- 
ences between bird-blood and mammalian blood who may not 
know a teal from a tern is as certainly a biologist. The naturalist 
takes the whole rural scene for his province, and is primarily 
interested in creatures as individuals; the biologist is predomi- 
nantly concerned to answer specific questions, and seeks general 
truths. The biological sciences are descriptive indeed, in the same 
sense, however, that the chemical sciences are descriptive for 
they use concepts like "genes," "evolution," "photosynthesis" 
which are as much the product of scientific inference as 
"atom" or "polymerization." Natural history, on the other hand, 
"describes" in the commonplace sense of the word; its concepts 
like "mating," "hunting," "feeding young" are those of ordinary 
thought, rarely the product of scientific inference. The naturalist 
is indeed a trained observer, but his observations differ from those 
of a gamekeeper only in degree, not in kind; his sole esoteric 
qualification is familiarity with systematic nomenclature. 1 

Natural history, as here differentiated from biology, seems at 
the present time to be of small and shrinking scientific significance. 
The naturalist has inevitably become dependent upon the deeper 
insight of the biologist so that (for example) questions of classifi- 
cation, after being his main concern since the sixteenth century, 
have been radically modified during the last hundred years by 
biological research into evolution and embryology. The introduc- 
tion of new and more rigorous techniques, making large use of 
the experimental method, has carved from the naturalist's former 
province such subjects as ecology and animal psychology. In any 
case, the observations of a Gilbert White are no more repeatable 
than those of a Marcel Proust, and partly for the same reason that 
their enduring interest resides in individual qualities of imagina- 
tion and literary skill applied to a particular social setting. The 
writing of natural history may continue, like that of the novel, ever 
different and ever the same, but the evolution from it of scientific 
biology could only happen once (or, more accurately, in successive 

1 These distinctions are, it is recognized, subject to innumerable qualifica- 
tions. In practice, many biologists share the naturalist's attitude in part, and 
many naturalists the biologist's; more exact experimental methods are being 
applied to field-work, etc. 


unique stages) just as the science of psychology could only emerge 
once from the physician's interest in mental disorders. 

The emergence of biology was certainly the leading contribution 
of the scientific revolution to the study of living things. A totally 
new kind of knowledge was thereby made possible, supplementary 
to that already obtained through the renaissance of natural 
history in the sixteenth century. Necessarily the first steps in this 
emergence were mainly descriptive, in studies of comparative 
morphology, minute anatomy and physiology, and the like. The 
description of an animal or plant which permits its identification 
may, however, be very different from a description of the same 
creature in relation to an appropriate group of scientific in- 
ferences. The structure of the hoof and leg of the horse may be so 
depicted, or portrayed in words, that the member may be easily 
distinguished from that of a dog; but to describe the same leg of 
the horse in terms of its evolution by extension of the middle digit 
of the foot and reduction of the side-digits is to embark upon a 
very different procedure. Or, to take an example from mineralogy 
(since this was a part of natural history until recent times) when 
metallic ores have been classified and labelled under such names 
as malachite, chalcocite or chalcopyrite, a new kind of knowledge 
is brought in by assigning to them their appropriate chemical 
formulae. Though these formulae are merely descriptive of the 
composition of the minerals, they enable comparisons to be made 
which are otherwise hidden. 

A mineralist who considers gypseous alabasters, plaster stone, lamel- 
lated gypsums, . . . and a great many other bodies as proper to be 
distinguished from one another, and who is able to ascribe any 
particular body to its proper species from considering its external 
appearance, is possessed of a particular kind and degree of know- 
ledge: He who besides being acquainted with the external appear- 
ances, is able to prove that all these different bodies are composed of 
a calcareous earth, united to the vitriolic acid; and thus makes several 
species of things coalesce together, and unite, as it were, under one 
general conception, hath a knowledge of these bodies different in 
kind and superior in degree. 1 

In the former example, appeal was made to the concept of 
evolution, in the latter to the concepts of inorganic chemistry. 

1 Richard Watson: Chemical Essays, vol. V (London, 1787), p. 127. Cf. 
L. J. M. CoJeby in Annals of Science, vol. IX (1953), p. 106. 


But the naturalist's description is sui generis, and all its complexity 
is no deeper than that of an unfamiliar vocabulary. 

At the close of the eighteenth century many of the procedures 
followed by the biologist in the course of his still mainly descriptive 
work as one may see from the investigations of Cuvier, of Haller, 
of Lavoisier, of John Hunter already anticipated those of the 
twentieth century. They were at least as "modern," by the same 
comparison, as those of the contemporary physicist and chemist. 
The great change has taken place in the intellectual framework 
within which such procedures are ordered. Biology had, indeed, 
successfully constructed an unco-ordinated group of scientific 
inferences, but it was still devoid of basic guiding principles: or 
rather, those which it possessed were derived from extra-scientific 
sources. Comparable in this state to mechanics before the seven- 
teenth century, the extent and the accuracy of the observational 
material collected together was by 1800 far greater. The science 
had followed a rather haphazard Baconian course, for although 
information had been compiled piecemeal with great diligence, 
the elucidation from it of keys to the understanding of living 
nature had hardly begun. The "laws of nature" were as yet 
purely inorganic: all the great theoretical principles of biology 
have won their dominion during the last century. This being so, 
it may be recognized that the chief difficulties confronting 
biologists during the critical period 1750-1850 that in which 
the influence of the natural-historian Linnaeus was at its height 
were those of conceptualization; as, again, had been the case in 
mechanics long before. The possibilities for significant theoretical 
thinking open to men who accepted the futilities of emboitement or 
the doctrine of successive catastrophes were as limited as those 
available to the Aristotelean opponents of Galileo. 

The similarity ceases, however, when the intrinsic difficulty of 
establishing the "laws" of biology is compared with that of 
clarifying the "laws" of mechanics. More mental effort is required 
to grasp the necessity for the concept of evolution than to see the 
plausibility of that of inertia; more important, it is possible to 
justify the former only by elaborate discussion of varied and 
obscure evidence. Darwin's Origin of Species has a very different 
character from Galileo's Discourses on Two New Sciences. Darwin 
devoted more than twenty years to the filling of note-books with 
materials bearing on his problem, materials which were in part 


made accessible to him by a long tradition of descriptive natural 
history, and which owed much to the taxonomical precision of 
his authorities. He was himself an expert taxonomist. 1 Similarly, 
the elements of the cell-theory were pieced together as the result 
of an even greater mass of cumulative observation, extending to 
the seventeenth century. The principles of biology could not 
spring from the analysis of common and simple observations, as 
did those of mechanics; and although it may truly be said that 
much current research owes little directly to the tradition of 
classificatory refinement stretching through and beyond Linnaeus, 
its origin lies in descriptive work to which that refinement was 
essential. A novelist does not need to be a lexicographer, but 
dictionaries are an essential foundation of good literature. 
Although biology has emerged from the natural history stage, its 
methods are not, and perhaps can never be, identical with those 
of physics. However great its development within laboratory walls, 
it must always have room for those techniques of description and 
discrimination with which the naturalists of the sixteenth century 
first strove to create a science. 

1 One reason for undertaking his monograph on the Cirrepedia (1851) was 
to prove to himself (and the world) that he was no mere philosophical biologist; 
though he afterwards doubted * whether the work was worth the consumption 
of so much time.' 


CHEMISTRY, as an integrated science with its own concepts, 
its own techniques, and its own area of applicability, is a 
product of the scientific revolution. The ancients, and their 
medieval successors, had no such distinct science, though they 
had much scattered empirical knowledge of this type, and some 
theoretical ideas that would now be described as of a chemical 
nature. Alchemy was not a primitive or pre-scientific chemistry, 
for it was both less (in the restricted range of its pretensions) and 
more (in its mystical affiliations) than a natural science. Chem- 
istry, like biology, grew from a number of distinct roots, and 
not by the expansion of a single tradition, as did mechanics and 
astronomy. Hence the attempt to classify the sources of chemical 
knowledge and theory in the early modern period becomes 
complex, and shows that these had little relation to the sub- 
divisions which now prevail. Researches of chemical significance 
occurred in mineralogy, in physiology, in physics, in pharma- 
cology, and most obviously in the development of technology. 
Likewise, the concepts used by writers on chemistry before the 
time of Lavoisier were often common property among natural 
philosophers, rather than exclusive to their own science. Such is 
the case with the four-element theory of matter, and with the 
corpuscularian " mechanical" hypothesis; both were physical, or 
rather cosmological, in origin. Chemistry, again like biology, 
shows that a science gains stature as it acquires its own specialized 
concepts as instruments of thought. Stage by stage, from the theory 
of the three principles in the sixteenth century, through that of 
phlogiston to the Lavoisierian notion of the chemical elements 
and their combinations, the science developed coherence and 

Hence the idea that there is a particularly chemical way of 
studying matter and its properties, whether inorganic or organic 
matter, was almost totally absent before the late sixteenth century, 
and even then gained ground but slowly. Early speculations about 



the nature or composition of matter, and about the processes 
involved when one kind of stuff is turned into another kind of 
stuff, were a part of physics, as little empirical as the rest of physical 
theory. They were scarcely at all connected with the practical 
knowledge of certain groups of craftsmen. In a similar manner 
it was far from obvious that a distinct science was required to 
explain how the bread that man eats is transmuted into flesh and 
bone. A pre-scientific physiologist might speak of " concoction" 
in the stomach, but the term, though frequently used by chemists, 
had no specific meaning. It was an empty word that described 
nothing and explained nothing. When, however, certain experi- 
menters adopted the belief that all metals are variously com- 
pounded of sulphur and mercury using the names sulphur and 
mercury in a particular sense distinct from that of ordinary 
language it does become possible to speak of a chemical attitude 
to substance. Robert Boyle frequently applied the word "chymist" 
in this way, as describing those who thought and worked in 
accordance with the three-principle theory. Otherwise the 
chemist was only distinguished from other men by the nature of 
his methods: 'What is accomplished by fire/ wrote Paracelsus, 
c is alchemy whether in the furnace or in the kitchen stove.' 1 
The chemist was indeed primarily a pyrotechnician, who knew (or 
tried to discover) how to obtain certain results by long and gentle, 
or short and fierce, heating. To the end of the seventeenth century 
chemical analysis was practically confined to destructive distilla- 
tion by fire, in which the substance to be analysed was forced to 
yield its waters, oils, sublimates, salts and caput morluum. In this 
sense the metal-refiner, the soap boiler and the distiller were 
chemists; the practices of more learned men in the early modern 
period were hardly less haphazardly empirical than theirs, and 
owed little more to the guiding influence of a distinctive theory. 
And, as chemical ideas were but slowly differentiated from those 
generally current in natural philosophy, so chemical techniques 
were very gradually differentiated from those of the kitchen and 
workshop. Even in the time of Lavoisier they still bore strong 
marks of their craft origin. 

Two possible approaches to the early history of chemistry 
are, therefore, bound to prove misleading, and to conceal the 

1 Alchemy to Paracelsus meant something much wider than the search for 
the secret of the transmutation of base metals into gold. 


significance of the development of the science during the period of 
the scientific revolution. It is futile to attempt to trace the progres- 
sive evolution from primitive beginnings into a modern form of 
a texture of chemical theory, because the idea that it is useful to 
apply a group of characteristically chemical concepts to the study 
of nature is itself modern. It is equally futile to derive chemistry 
from the elaboration of certain techniques of investigation, firstly 
because it is doubtful whether these enabled useful empirical 
facts to be discovered before a late date, and secondly because the 
intellectual background to the refinement of technique is far more 
significant than the refinement itself. If modern chemistry is not, 
as mechanics is, the result of the progressive emendation of an 
autogenous conceptual structure, it is also not that of purely 
deductive reasoning applied to "natural history" information 
collected about the properties of minerals, acids, alkalis, etc. 
though this view seems to contain more truth than the former. On 
the other hand, two analogous questions may usefully be asked. 
What attempts were made to account for changes in the properties 
of bodies effected by various manipulations (mainly with the aid 
of heat) in the light of existing scientific theory? How successfully 
were techniques adapted or invented with the double object of 
advancing technology and understanding? By asking questions of 
this form it is possible, without plunging into confusion, to 
recognize the indubitable facts that chemistry was always an 
eminently practical science, as well as a branch of natural 
philosophy, and that it lacked (before Lavoisier) a coherent 
conceptual scheme. 

To state the problems in such terms is not to deny that theory 
and practice were interdependent, or that individual chemists like 
Boyle might both add to factual knowledge, and seek for an ex- 
planation of chemical phenomena in current scientific thought. 
It does, however, admit that these two strands in the history of 
chemistry are logically distinct. This is very clear in the late 
medieval period. Then, natural philosophers were engaged in try- 
ing to fit the known facts of chemical change into the pattern of 
Aristotelean ideas concerning the nature and properties of matter, 
exactly as, more assiduously, they tried to arrange the facts of 
physics and astronomy according to the same pattern. Meanwhile, 
the pattern itself preserved its character, and no essentially new 
ideas were brought out. By contrast, empirical knowledge of the 



phenomena of chemistry increased rapidly during the same period, 
owing progressively less to a remote Hellenistic ancestry. In glass- 
working, in the smelting and refining of metals, in dyeing and 
leather-dressing, in military pyrotechnics, in the distillation of 
alcohol and other " waters," in the glazing of pottery and the 
preparation of pigments generally, in the manufacture of medica- 
ments of all kinds briefly, in every aspect of chemical technology 
the European world of about 1500 enjoyed a consistent superiority 
over the Graeco-Roman. In the millennium between the fall of 
Rome and that of Constantinople alcohol and the mineral acids 
were discovered, saltpetre was distinguished from soda (this made 
gunpowder possible), many new minerals were recognized, 
named, and their usefulness exploited, the known compounds of 
metals increased in number, chemical apparatus assumed a defi- 
nite form, the control of furnaces was improved, and operations 
like reduction and oxidation were mastered (though their nature, 
of course, remained unknown) . Some of this knowledge emanated 
from a Graeco-Egyptian tradition, centred on Alexandria; im- 
portant elements were derived from India and China, but prac- 
tically nothing came from the academic scientific line of the 
ancient world, stemming from Plato and Aristotle through Pliny. 
The whole was synthesized and further advanced by the Islamic 
peoples, who were excellent chemical craftsmen, and further con- 
siderable progress was made in the Latin West from the twelfth 
century onwards. As some of the important sources, such as the 
writings of Geber and the Book of Fires of Marcus Graecus, are 
now accredited to Latin compilers who made use (to a degree 
which cannot be exactly estimated) of unknown originals, the de- 
tailed ascription of inventions in the chemical arts to Byzantium, 
Islam, or Latin Europe is often impossible. But it is quite certain 
that they are post-classical. 

Little reflection of this growing empirical knowledge is to be 
found in the writings of medieval natural philosophers, with the 
rare exception of Roger Bacon. Only such discoveries as were 
possibly effected, or alternatively adopted, by the alchemists (like 
the preparation of mineral acids and the solution of metals in 
them) were of interest. More was done by physicians, with regard 
to pharmacologically useful discoveries. The third class of writing 
which gives an insight into medieval chemical technology consists 
of recipe books of many types, among them the different versions 


of the Mappa clavicula, the Note on various crafts of the monk Theo- 
philus (c. 1200), the Book of Fires already mentioned, and the Book 
on colour making of Peter of St. Omer (c. 1300). This class becomes 
much fuller from the fourteenth century. While, therefore, texts 
in this group may be drawn upon to form a picture of the level of 
factual knowledge concerning the preparation and properties of 
substances attained by the close of the middle ages, it is almost 
useless to look to them for the beginnings of a chemical attitude. 

The literature of alchemy is copious, and many have searched 
in it for the beginnings of chemistry. There the grain of real know- 
ledge is concealed in a vast deal of esoteric chaff. The view that 
alchemy represents the pre-history of chemistry (as developing 
chemical techniques, and factual knowledge of substances) is, after 
all, primarily based on the fact that such information is frequently 
set out, in the surviving texts, in an alchemical context. But there 
is no means of knowing that, because a discovery or an observation 
is first reported by an alchemist, it was made as a result of his 
inquisitive experimentation. The most remarkable feature of all 
alchemical writings is that their authors prove themselves utterly 
incapable of distinguishing true from false, a genuine observation 
(according to our modern knowledge) from the product of their 
own extravagant imaginations. It seems unnecessary to give them 
credit for making important truths known, when they were so 
obviously incapable of discrimination. It is certain that many 
practices and observations of alchemy were older than alchemy 
itself, just as observational astronomy preceded astrology. It is also 
certain that in the medieval period much knowledge was gained 
outside the alchemical context which was restricted, almost ex- 
clusively, to metallic compounds. Taken together, these facts 
suggest that were the early history of practical, industrial chem- 
istry more fully revealed, the inventiveness attributed to the 
alchemical dream would be found exaggerated. Some of the dis- 
coveries attributed to it may well have come from a differently 
directed experimentation; some alchemists were also physicians. 

The theoretical contribution of alchemy to science was very 
small. Its own pretensions forbade the application of the usual 
notions of natural philosophy to the phenomena studied, and 
despite the interest of some philosophers in the art, there were 
always others who derided it. The theory of transmutation held 
by the later alchemists was originated by Jabir ibn Hayyan and 


al-Razi. It was made known to Europe in the twelfth century. 
They believed that all metals are composed of " philosophic" 
sulphur and "philosophic" mercury, which could be obtained by 
art from the base metals, and recompounded to form the precious 
metals: 1 

Therefore if clean, fixed, red, and clear Sulphur fall upon the pure 
Substance of Argentvive (being itself not excelling, but of a small Quan- 
tity, and excelled) of it is created pure Gold. But if the Sulphur be clean, 
fixed, white and clear, which falls upon the Substance of Argentvive, 
pure silver is made . . . yet this hath a Purity short of the Purity of 
Gold, and a more gross Inspissation than Gold hath. 2 

It is enough to say that this theory was never developed (save in 
mystical embroidery), that it was never attached to any sound 
body of empirical knowledge, and that its persistence was the 
greatest obstacle to the development of a rational chemistry. 

In any case, the pursuit of alchemical chimaeras had long ceased 
to bring any useful information to light by the beginning of the 
sixteenth century. The significant event of this time was the 
emergence, from the obscure and laconic notes of recipe-books, of 
literate descriptions of the operations of chemical industry, espe- 
cially those connected with metallurgy. These books have been 
discussed already (pp. 221-3). Here at last was metallurgical 
chemistry (and much more) free from the extravagances of al- 
chemy. Here was a clear discrimination between fact and fiction 
with regard to the " transmutations " effected by chemical art. 
Theoretical speculation was almost entirely absent from these 
accounts, Agricola alone being notable for an attempt to explain 
his observations in terms of Aristotelean science, without, however, 
improving its texture. Thus was founded a serviceable and lasting 
tradition, which after a recession lasting through a couple of 
generations (those most subject to the influence of Paracelsus) was 
again revived by the scientific societies. From that time the 
academic study of industrial chemistry was never neglected. 
Eighteenth-century chemists like Black and Macquer were closely 
associated with it. Lavoisier did an enormous amount of work as a 
government consultant, reforming the administration and chem- 

1 These principles were ultimately compounded of the Aristotelean ele- 
ments, but could be procured, as it were, as intermediate states. 

2 Argentvive = mercury. Works of Geber, Englished by Richard Russell i6"/8, 
Ed. by E. J. Holmyard (London, 1928), p. 132. 


istry of the French explosives industry. And it may safely be said 
that the rapid extension of chemical research in the nineteenth 
century and later would have been impossible but for its close 
connection with manufacture. Much earlier the remarks of the 
Fellows of the Royal Society, especially Robert Boyle, on the 
necessity of close attention to trade methods give a hint of a source 
from which much was learnt not least, in the way of suggesting 
the type of problems which might most usefully be attacked. For 
on this, it is obvious, modern chemistry largely depended for its 
early success. The only problems which the early chemist could 
hope to solve in a rational way were the simple ones dealing with 
the oxidation of metals, the calcination of limestone, quantitative 
analysis of simple inorganic compounds which were in fact posed 
by the basic chemical industries. However stimulating the fascin- 
ating questions suggested by more elaborate chemical changes 
might be, including those raised by the known connection be- 
tween chemistry and medicine, answers to them remained far 
over the horizon until such time as organic chemistry slowly 
increased its scope through the mastery of inorganic reactions. 

Though the endeavour to render physiology a branch of chem- 
istry inevitably failed in the sixteenth and seventeenth centuries, 
nevertheless it did on the one hand promote the development of 
a distinctively chemical attitude to physiological and other prob- 
lems, arid on the other led to extensive exploration of chemical 
compounds with the object of using them as drugs. Inorganic 
medicaments were not new. Salt has always been collected as a 
necessity for life; antimony sulphide, copper salts, sodium carbon- 
ate, ochres, alum, and other minerals are prescribed for various 
purposes in the Papyrus Ebers (sixteenth century B.C.). 1 Possibly less, 
and certainly not greater, faith was attached to them in late 
medieval Europe. These were, however, natural substances, not 
the factitious products of art, few of which had yet been identified 
with naturally-occurring minerals. 

Roger Bacon had taught that medicine should make use of 
remedies provided by chemistry, but it was not until the sixteenth 
century that his idea was fully developed, by Theophrastus 
Bombastus von Hohenheim (1493-1541), called Paracelsus, the 
founder of iatrochemistry (medical chemistry). His was not in 
any sense a modern mind. He believed in the philosopher's stone. 
1 H. E. Sigerist: History of Medicine, vol. I (Oxford, 1951), p. 343. 


He believed in the alchemical theory of transmutation, and in 
others yet more wonderful: 

If the living bird be burned to dust and ashes in a sealed cucurbite 
with the third degree of fire, and then, still shut up, be putrified with 
the highest degree of putrefaction in a venter equinus so as to become 
a mucilaginous phlegm, then that phlegm can again be brought to 
maturity, and so, renovated and restored, can become a living 
bird. . . .! 

He had in full measure the faculty for self-deception characteristic 
of the Hermetic tradition. For him, the physician and chemist 
were one, a magus whose operations influenced the natural and 
supernatural worlds together. In the words of Lynn Thorndike: 

for Paracelsus there is no such thing as natural law, and consequently 
no such thing as natural science. Even the force of the stars may be 
side-tracked, thwarted or qualified by the interference of a demon. 
Even the most hopeless disease may yield to a timely incantation or 
magic rite. Everywhere there is mystery, animism, invisible forces. 2 

But he was an iconoclast. He poured scorn upon the revered 
writings of Galen and other authorities. For their dietary rules and 
herbal preparations he wished to substitute new drugs purified by 
the action of fire. 'The work of bringing things to their perfection 
is called alchemy, and he is an alchemist who brings what nature 
grows for the use of man to its destined end.' Vulcan was to be his 
apothecary. In his medical practice he made much use of chemical 
preparations of herbs (to extract their virtue), laudanum, alcohol, 
mercury and metallic compounds, obtained by techniques familiar 
to alchemists. In theory, he added salt to the other alchemical 
principles, sulphur and mercury; otherwise his theoretical notions 
were fully as chaotic as those of other alchemists. 

No great reformation was to be expected from Paracelsus' in- 
coherent, obscure, megalomanic writings. Yet the iatrochemical 
school flourished; the greater part of what was done up to Boyle's 
time may be attributed to it, and during two generations chemists 
were to a greater or less degree Paracelsians, known by their 
attachment to the three principles. Indeed Paracelsus' theses with 

1 A. E. Waiter Hermetical and Alchemical Writings of Paracelsus (London, 1894), 
vol. I, p. 121. 

2 History of Magic and Experimental Science, vol. V (New York, 1941), p. 628. 


regard to medicine, that useful drugs could be made in the labora- 
tory, and that there was room for bolder experiment in the treat- 
ment of disease, were obviously correct when purged of the 
fantasies and occultism with which, in him, they were always 
enmeshed. No one could doubt the efficacy of Glauber's sal mirabile 
(sodium sulphate), and long before Paracelsus' time the adminis- 
tration of mercury had been proved a specific against the common 
and dangerous disease, syphilis. 1 The ambitions of the iatrochem- 
ists were to reveal the chemical nature of physiological processes, 
by discovering the secret laws by which the combinations and 
recombinations of matter are governed, and to enlarge the list 
of compounds known to be effective against disease. These were 
rational objects, though the manner in which they were pursued 
was haphazard. Paracelsus had done little in chemistry himself. His 
successors devoted themselves more fully to mastering the tech- 
niques which would yield hitherto unknown substances. They did 
not hesitate to draw, where they could, upon the experience of 
industrial chemistry. 

These men were the "chy mists" or "spagyrists" known to 
Boyle and his contemporary philosophical chemists. They were 
men of learning and wrote Latin. Their view was narrow, being 
limited by the doctrine of the three principles, and they were 
often subject to the delusions of alchemy, but their books were 
meant to be understood. They created no secret language. 
Instead they began to describe, as plainly as their knowledge and 
terminology allowed, how the operations of chemistry are per- 
formed, from what materials and by what methods a large number 
of compounds are prepared, and for what purposes they might be 
employed. They began to compare the method used in one case 
with that used in another, to detect analogies between different 
compounds, and to try to explain what happened when a chemical 
reaction occurred by means of concepts which they invented or 
adapted. Here was the beginning both of a " natural history" of 
chemistry, and of a chemical theory. 

Andreas Libavius (d. 1616), the first important iatrochemist 

1 Salivation was condemned by many non-iatrochemical physicians, 
because death was so often caused by mercurial poisoning. Medical faculties 
forbade the use of iatrochemical methods for well over a century, Sir Theodore 
de Mayerne, James I's physician, being expelled from Paris on this account. 
They were gradually admitted to official pharmacopoeias during the seven- 
teenth century. 


after Paracelsus, refused to number himself among the latter's 
followers. From his Alchemia (1597) he claimed, justifiably, to 
have omitted the magical and superstitious elements introduced 
by Paracelsus, and to have purified the art of his figments and 
phantasms. * Unhappy would chemistry be, if it had been founded 
by Paracelsus. . . . Filthy are the Paracelsian lies and blasphemies.' 
Nevertheless, he still believed in transmutation. The Alchemia was 
Libavius' most important work, though he admitted that it was 
largely compiled from other writers. 1 It is a methodical account 
of the chemical knowledge and laboratory technique of his time. 
He described many antimonial and arsenical compounds, 2 sul- 
phurous acid, the stannic chloride (SnCl 4 ) known as "Libavius' 
fuming liquor," the extraction of many oils, waters and essences, 
and the analysis of mineral waters. In the second edition there 
is a long discussion, with wood-cuts, of the design of a chemical 
laboratory. From such a work as this it was but a step to the 
treatment of chemistry simply as an auxiliary of medicine. This 
is the attitude of Jean Beguin in his Tirocinium Chymicum (1610) 
who thus defined his subject: 'Chymistry is the Art of dissolving 
natural bodies, and of coagulating the same when dissolved, and 
of reducing them into salubrious, safe, and grateful medicaments.' 3 
The Tyrocinium is a very straightforward recipe book, forerunner 
of many others of the same kind. 

The greatest of the iatrochemists, Johann Baptista van Helmont 
(1577 or 1580-1644) was a figure in some ways only less flam- 
boyant than Paracelsus, for he also gave his imagination free 
licence. His criticism of academic medicine was more reasoned 
than Paracelsus', but not less severe. 'The art of healing,' he 
thought, " was a mere imposture, brought in by the Greeks. . . . To 
this day the schools do scarcely acknowledge any other remedies 
than blood-letting and their stock of laxatives; their whole 
endeavour is with bleeding, evacuations, baths, cauteries, sweats, 
so that they presume to cure all ills of the flesh by weakening the 

1 There are two editions, Alchemia Andrea Libavii Med. D. Poet. Physici 
Rotemburg, etc. (Frankfort, 1597), p. 424; and the large folio with wood-cuts 
Alchymia Andrea Libavii, recognita, emendata, et aucta etc., (Frankfort, 1606), 
pp. 196 -f 402 -f 192. 

2 This, of course, was before the Triumphal Chariot of Antimony of the pseudo- 
Basil Valentine. 

3 Tyrocinium Chymicum, or Chymical Essqyes Acquired from t(ie Fountaine of 
Nature and Manuall Experience [trans, by Richard Russell] (London, 1669), p. i. 
This primer was deservedly popular. 


body and its strength, and by corrupting the blood.' 1 Despairing 
of such methods, van Helmont turned to chemistry because 
insight into nature generally, and the workings of the human body 
in particular, could only be gained through a sound knowledge 
of substance. To this end he developed a totally novel theory by 
which he proved himself far more than a mere chemist like 
Libavius. In the first thirty chapters of the Ortus Medicirue he 
sketched out a new natural philosophy, often obscure and 
muddled, and more than tinged with a naive credulity, which 
was as much directed against Aristotle as against Galen. His 
speculations ranged far beyond the bounds of chemistry and 
medicine, to meteorology and the causes of earthquakes. The 
most important of them was his contention that there are only 
two elements, Air and Water. Fire he did not regard as a body, 
and therefore it could not be an element. All solid bodies, includ- 
ing the earths, were generated from water by the action of seeds 
or ferments: The first beginnings of bodies, and of corporeal 
causes, are two and no more. They are surely the element Water, 
from which bodies are fashioned, and the ferment by which they 
are fashioned.' 2 These divinely created ferments were the specific 
organizers of water, the prima materiel, into minerals as well as 
living things; they were immaterial, though the seeds to which 
they gave rise were not. Van Helmont referred in support of this 
doctrine to the success of chemists in reducing solid bodies to 
an " unsavoury water" (e.g. by solution in acids, followed by 
neutralization); to the fact that fishes are nourished solely on 
water (!); and to his famous experiment on the growth of a 
willow tree in a tub of earth. Although nothing but water was 
added, the tree gained 164 Ib. weight in five years without any 
diminution of the earth in which it was planted; water had 
clearly been transmuted into solid matter by the action of the 
"seed" in the tree. 3 Like Boyle later, van Helmont attacked the 
three principles of orthodox chemists on the ground that some 
bodies could not be resolved into them. He accepted the existence 
of vacua in solid matter: for this explained how metals could be 

1 Ortus Medicina, Col. I, 6; III, 7. This collection of all van Helmont's 
works was published by his son at Amsterdam in 1648. An English translation 
by John Chandler appeared in 1662. 

2 Ortus Medicirue (Lyons, 1667), p. 23. 

3 Ibid., p. 68. The experiment had been suggested by Nicholas of Cusa in the 
fifteenth century. 


more dense than water. Air, however, could not be turned into 
water, even by great compression, and was therefore a distinct 

False thinking on these matters was, in van Helmont's view, the 
main cause of error in science down to his time. He also attached 
great importance to two new conceptions, for which he coined 
new names. One was "Bias" a sort of intrinsic motion in the 
stars and planets (which thereby affected the earth beneath), in 
the air, and in man. The other was "Gas," which name had 
a significance quite other than that now attached to it. Van 
Helmont's gas was simply a form of water, and he used the idea 
to confirm further his theory that water was the prima materia. 
Any matter, such as water vapour, carried into the extreme upper 
air, was turned into gas (i.e. was finely divided, since 'gas is far 
more subtle than vapour, steams, or distilled oils, although much 
denser than air') by the sharp cold and the "death" of the 
ferments. Then this gas might itself condense into vapour and fall 
as rain: at any rate, it was the chief cause of meteorological 
phenomena. Again, when substances burnt, the greater part of 
them disappeared as gas, which was also water, or 'water 
disguised by the ferments of solid bodies.' The point of van 
Helmont's observation, that there is only i Ib. of ash obtained 
from 62 of charcoal, the rest disappearing as spiritus Sylvester (wild 
spirit), seems to be that the charcoal itself is gas, i.e. water. 1 
He knew that if the escape of the spirit was prevented, by en- 
closing the charcoal in a sealed vessel, combustion would not 
occur. This led him into his celebrated definition: 'This spirit, 
hitherto unknown, which can neither be retained in vessels nor 
reduced to a visible body (unless the seed is first extinguished) I 
call by the new name Gas.'* Thus van Helmont's element-theory 
might be symbolized 

water + seed (ferment) > substance 
and with his concept of gas this became 

water > vapour * gas * water, 
and (water + seed) > substance * gas * water 

1 He had already "proved" that ash could be turned into water. 

2 Cf. Ortus Medicine " Progymnasma meteori," "Gas aquae," "Complexio- 
nurn atque mistionum elementalium figmentum." 


In other words, the concept of gas was simply a complexity added 
to the doctrine which van Helmont most wanted to drive home, 
that is: water is all. Its main function was to explain the otherwise 
rather awkward fact that the products of combustion do not 
normally include much water-vapour. Just as he had to deny 
corporeal status to flame and fire (which could not be supposed to 
come from, or turn into, water) so van Helmont had to invent 
gas as a form of water. 

He noticed that gas might be evolved from a combination of 
substances, or a substance acted upon by a ferment, though not 
if the substance was taken by itself. Thus he found that saltpetre 
alone yielded no gas, but that gunpowder does hence the violence 
of the explosion. Grapes yielded a gas when bruised and fermented. 
He also applied the name gas to the red fumes given off when 
nitric acid reacts with silver, to the product of the reaction between 
sulphuric acid and salt of tartar, to the furncs given off by burning 
sulphur, to flatus, to the poisonous substance which collects in 
mines and extinguishes candles, etc. While unable to recognize 
and classify these different gases systematically, he was of course 
able to make qualitative distinctions between nitric oxide, sulphur 
dioxide, carbon dioxide, mixtures of hydrogen and methane, and 
this particular attention to " fumes" (which must have been very 
often observed in the past) was perhaps van Helmont's best 
service to chemistry. But there is no evidence that he ever ad- 
vanced beyond the notion that gases were substantially water, 
modified by the characteristic of immaterial ferments: indeed, he 
does not seem to speak of "gases" at all, as a plurality. 

It has often been said, and rightly, that the long failure to 
understand the role of the common gases was a grave obstacle 
to the development of chemistry. It seems, however, that van 
Helmont, despite the praise frequently meted out to him as the 
first student of gases, really did little to lessen this obstacle. The 
modern notion of gas involves two propositions, the second being 
logically unnecessary, but required by experience: (i) There is a 
state of matter in which the particles are separated and free to 
move, rendering the matter tenuous and elastic; (2) Some forms 
of matter are normally encountered only in this state. Now the 
first of these propositions, though it was little developed theoretic- 
ally before the nineteenth century (having been disregarded, for 
the most part, by the practical chemists who really worked out 


something of the importance of gaseous elements in chemical 
combinations) would not have seemed at all unfamiliar to 
seventeenth-century physicists, to whom the particulate nature 
and elasticity of "airs" were commonplaces. Their notions of 
"factitious airs" and "elastic fluids" clearly foreshadowed the 
modern physical idea of a gas. But they had no corresponding 
chemical conceptions. The pivotal discovery, the apprehension that 
made Lavoisier's chemistry possible, was the enunciation of the 
second proposition in a chemical setting. It was the fact that some 
participants in chemical reactions both elementary and com- 
pound could normally be isolated in the gaseous state only, 
though capable of entering into solid and liquid combinations, 
which was of strategic significance. 

Therefore van Helmont's view of gas as a state of matter 
intermediate in fineness between a vapour and the clement air, 
and as the fume, smoke or spirit evolved from a chemical process, 
was of very little profit in itself. While his ideas helped to encourage 
interest in these curious products, there was little real merit in 
the attachment of a special name to something so vaguely con- 
ceived, and so deeply involved in an unacceptable doctrine of 
watery transmutations. Chemists especially the English con- 
tinued to speak of "airs" and "elastic fluids" with good reason; 
they chose rather to believe that gases were modified air than (with 
van Helmont) that they were modified water, and air an inert 
element. It cannot be said that they preferred the less plausible 
of the two hypotheses. To have converted the Helmontian view 
"gas is a state of water" into the statement "gas is a form of 
material substances, distinct from air, which participates in 
chemical reactions" was impossible. If van Helmont was right 
(as we now know) in suggesting that gas is not air, it was far more 
obvious to contemporaries that he was wrong in maintaining that 
gas was a phase in water > substance > water transmutations. 
Chemists like Boyle could make nothing of his Gas and Bias. 
They could not see that of these two whimsical notions, the former 
was far more worthy, since to them the single-element doctrine in 
which van Helmont's gas is involved was incomprehensible. Even 
to hint that the subsequent neglect of van Helmont's work on gas 
retarded the development of chemistry is to misunderstand the 
content of his thought, and to convey a thoroughly misleading 


About the middle of the seventeenth century the position in 
chemical theory (to use what is still an anachronism) was that the 
Aristotelean doctrine, now moribund and opposed to the broad 
trend of the scientific revolution, was still respectable; practising 
chemists, as a class, stood by their three principles and the general 
tenets of iatrochemistry; van Helmont's single-element theory 
aroused much interest, but won few adherents. Meanwhile, a 
fourth approach to the problems of chemical combination, based 
on the mechanical, particulate view of matter was taking shape, 
and was soon to be developed elaborately by Robert Boyle. 
Factual knowledge of chemical reactions and processes had also 
ramified considerably since the time of Libavius. Van Helmont 
himself, for all his natur-philosophische outlook, was a skilled prac- 
tical chemist, who reported a good number of new preparations. 
He taught that matter was indestructible, illustrating this belief by 
the recovery of the original weight of a metal from the compounds 
in which it was apparently disguised. 1 It is said that he made much 
use of the balance: his famous tree-experiment shows how deceptive 
quantitative methods may be when applied within an inadequate 
conceptual scheme. A younger iatrochemist (who also pursued 
the philosopher's stone) was Johann Rudolph Glauber (1604-70). 
He described for the first time the preparation of spirit of 
salt (HC1), sodium sulphate, and perhaps chlorine. Glauber had a 
sound insight into certain types of chemical reaction, such as double 
decomposition; for example, he explained the formation of " butter 
of antimony" with sublimation of cinnabar from stibnite heated 
with corrosive sublimate by saying that the spirit in the latter, 
leaving the mercury, preferred to attach itself to the antimony in 
the stibnite; the mercury then united with the sulphur in the 
stibnite to form cinnabar. 2 From this example it is also clear that 
Glauber employed the concept of chemical affinity he understood 
that one unit in a reaction might attract 'another more than a 

1 ' Since nothing is made from nothing, the weight [of one body] is made 
of the equal weight of another body, in which there is a transmutation of 
matter, as well as of the whole essence' (Prog. Meteori, 18). Van Helmont's 
argument seems to be, that the same weight of prima materia (water) is repre- 
sented by equal weights of any substance, irrespective of their densities. 

2 i.e., Sb 2 S 3 + 3HgCl 2 = 2SbCl 3 -f sHgS. Double decomposition in this 
same reaction was indicated rather less clearly by Beguin in the 1615 edition 
of his Tyrocinium Chymicum. Cf. T. S. Patterson in Annals of Science, vol. II 
(London, 1937), p. 278. 


In 1675 there was printed for the first time a new textbook on 
chemistry by a practical man, Nicholas Lemery (1645-1715), 
which remained popular for upwards of half a century. The title 
of the Cours de Chymie contenant la maniere de faire les operations qui 
sont en usage dans la Medecine sufficiently indicates its purpose. It 
was a straightforward recipe-book, dealing first with the metals, 
then with salts, sulphur and other minerals, and finally with 
preparations obtained from vegetables and animals. Lemery was 
not given to theorization, but he taught that there were, in addi- 
tion to the three active principles mercury (spirit), sulphur (oil) 
and salt, two passive principles, water and earth. He also accepted 
the theory due to Otto Tachenius that salt acid -f- alkali, and 
occasionally followed the particulatc ideas of Descartes. The Cours 
de Chymie was the most successful of many similar practical books 
published at about the same time: an English example is George 
Wilson's Compleat Course of Chymistry (? London, 1699). By the end 
of the seventeenth century the best accounts of experimental 
chemistry were those written with medical applications in mind, 
and though the old, esoteric iatrochemistry deriving from Para- 
celsus had perished, future progress was to owe much to physicians 
and apothecaries, among them Boerhaave, Cullen, Scheele and 
Black. It is of significance also that the teaching of chemistry in 
universities, beginning c. 1 700, everywhere placed it as an auxili- 
ary to medicine. Even at the close of the eighteenth century most 
of Black's pupils at Edinburgh were medical students. 1 From the 
time of Boyle to that of Priestley and Cavendish the role of the 
"amateurs" in chemistry was relatively insignificant, and the 
reason is not far to seek. This was a period of rapid practical 
development in the subject, but of minor theoretical expansion. 

It is therefore appropriate now to turn to this last of the great 
philosophical chemists, Robert Boyle, who is one of the most 
enigmatic figures of the scientific revolution. There can be no 
doubt that he was one of its leading personalities, nor that he made 
wide, and incisive, use of the new ideas maturing in his time. 
Whether he was himself capable of any major creative act in 
scientific thought is more arguable. Possibly his originality (but 
not his perseverance) as an experimenter has also been exagger- 
ated; it is difficult to estimate accurately, since Boyle's works are 

1 Cf. the interesting paper by Dr. James Kendall in Proc. Roy. Soc. Edin., 
Section A ? vol, LXIII (Edinburgh, 1952), p. 346 et seq. 


perhaps the first to be filled with descriptions of experimental 
research. These books, on which his fame was established, are 
hugely prolix and sometimes tedious, containing masses of ob- 
servations haphazardly selected and arranged, through which the 
reader has to pick his way in search of the point of the discussion, 
often to find that Boyle has been unable to make up his own mind. 
Yet they are always redeemed by the sense of a sharp and con- 
tinuous purpose, a far-reaching breadth of learning, and a humility 
in face of the facts of nature that forbade dogmatism. 

The task Boyle set himself was to examine philosophically the 
natural phenomena made known by chemical art; to determine 
the underlying nature of the material transformations of which 
a cumulative description had been built up since the time of 
Libavius, and of the processes by which they were brought about. 
He undertook to prove to philosophers that chemistry could be 
more than a collection of recipes, and to the "chy mists'* that in 
revealing nature's secrets they would have a more noble aim than 
the concoction of medicines. Not that Boyle despised the applica- 
tion of chemistry to medicine. He regularly dosed himself and his 
friends, and welcomed any new compound that promised thera- 
peutic value, but he was aware that science as a whole is greater 
than the cure of disease. Boyle wrote no textbook of chemistry, 
like Lemery's, rather he usually assumed such a level of knowledge 
in his readers; nor was he greatly interested in the piling up of 
more and more empirical knowledge for its own sake. Almost 
always he wrote with a definite problem in mind, some aspect of 
his ambition to restore natural philosophy as a unified whole, in 
which chemical knowledge should play its due part. He sought to 
build a bridge between chemistry and physics, the two sciences 
concerned with the properties of matter, which ought to start 
from common ground and be explicable one in terms of the other. 
In this respect Boyle had much in common with van Helmont, 
whom he greatly admired (while admitting his frequent inability 
to comprehend him); but whereas van Helmont had criticized 
natural philosophers for their ignorance of ideas to which he him- 
self had been brought by his own quasi-Paracelsian development, 
Boyle proceeded quite differently. Essentially a physicist looking 
at chemistry, Boyle sought to demonstrate that the facts and pro- 
cesses of chemistry were explicable in terms of the corpuscularian, 
mechanical hypothesis of matter which he had adopted. 


In the first of his major works to be printed, which is also the 
most widely read, this is certainly not very clear. The purpose of 
the Sceptical Chymist (1661), as its title suggests, is negative, not 
positive. It was to clear the ground of the three theoretical atti- 
tudes to chemistry which were then in vogue. Boyle disposed 
rapidly of the four Aristotelean elements, for they were no longer 
plausible entities (at least to the progressive experimental 
scientist). 1 His main attack was upon the three principles of the 
orthodox chemists, his real target. In this connection there was 
nothing novel in his own definition of a chemical element, nor in 
his insistence on the importance of discovering what the ultimate 
constituents of compound bodies are. 2 He argued that none of the 
chemists' principles could be extracted from metals like gold or 
mercury; that their criterion of analysis by fire was in any case 
faulty, since it could not divide glass into its known constituents, 
sand and alkali. He pointed out (like van Helmont) that the 
natures of bodies are not changed by entering into combinations, 
since the same bodies could sometimes be recovered separately 
in their original state. He emphasized acutely the illogicalities 
and contradictions in which the ideas commonly entertained by 
chemists were involved. This criticism was warrantable, but in the 
Sceptical Chymist Boyle equally proved that he could create nothing 
to take the place of that which he would destroy. No more than 
any other contemporary did he believe that ordinary substances 
gold, mercury, sulphur were elements, though they resisted 
analysis. He used van Helmont's tree-experiment (which he re- 
peated) to show that vegetable matter could be formed from water 
alone, without the participation of earth and fire, or salt and 
sulphur, but he did not believe that all things were made of water. 
In the end Boyle failed not only to draw up his own list of chemical 
elements, but even to decide definitely whether such simple 
substances do exist at all. 

1 However, they were by no means dead. The four Aristotelean elements 
were still to recur in the eighteenth century, whether in Chambers^ Dictionary 
or in P. J. Macquer's Dictionnaire de Chymie, where it is said (s.v. Umens) 
* on doit regarder en chymie le feu, Pair, Peau et la terre, comme des corps 

2 Cf. The definition of van Helmont (Prog. Meteori, 7): 'An element would 
cease to be a simple body, if it were divisible into anything prior, or more 
simple. But nothing among corporeal things is granted to be prior to, or more 
simple than, an element.' Boyle did not claim any originality for himself, 
rather admitting that his definition was a common one. 


There was, indeed, sufficient reason in his corpuscular physics 
why he should have been doubtful, why he should have thought 
that anything might be transmuted into anything else, by nature 
if not by art. 1 Some of the evidence is set forth in the Sceptical 
Chymist: Boyle believed, with most of his generation, that metals 
and minerals like saltpetre "grew" in the earth. These substances 
were not themselves elements; neither were they formed from 
pre-existing elements, for such elements could not be traced in the 
earth where the growth occurred. 'From thence' wrote Boyle 
'we may deduce that earth, by a metalline plastick principle 
latent in it ["seed"], may be in process of time changed into a 
metal' a common enough opinion. 2 From a survey of pheno- 
mena of this kind he came to the conclusion that transmutations 
in the chemical sense were possible by means of this "plastic 
power" in the earth, as also by the "seminal virtue" in seeds (for 
the salts etc. in wood were certainly not present as such in the 
water with which the tree was nourished). However puzzling this 
might be from the chemist's point of view, it was not at all inex- 
plicable to the physicist in Boyle, for his physical theory of matter 
taught him that all substances are made up of the same funda- 
mental particles. 3 Since, therefore, substances differ from one 
another only in the 'various textures resulting from the bigness, 
shape, motion and contrivance of their small parts, it will not be 
irrational to conceive that one and the same parcel of the universal 
matter may, by various alterations and contextures, be brought 
to deserve the name, sometimes of a sulphureous, and sometimes 
of a terrene or aqueous body.' 4 

The theory of matter which Boyle favoured led him to believe 
(as he acknowledged in the early pages of the Sceptical Chymist) 
that in its basic and primitive form matter existed as 'little 

1 One transformation in which Boyle was naturally very interested was that 
of base metals into gold. Like Newton he seems never to have been altogether 
confident that this transmutation, though theoretically attainable, was actually 

2 Works (London, 1772), vol. I, p. 564. Boyle cited Cesalpino and Agricola 
for the statement that metals reappear in previously worked-out veins. For 
Agricola's belief that metals are generated from the Aristotelean elements 
earth and water, cf. De re metallica (New York, 1950), p. 51, note. 

3 A modern analogy would be the proposition that the chemical element is 
an unsound and illogical concept, since all are composed of the same sub-atomic 

4 Works (London, 1772), vol. I, p. 494. 


particles, of several sizes and shapes, variously moved. 5 These 
were further organized into 'minute masses or clusters/ being 
the 'primary concretions' of matter, some of which were in 
practice indivisible. Hence the clusters that compose gold, being 
inviolable by the ordinary chemist's art, could always be recovered 
from any compound of the metal. But a mass of such corpuscles 
was not an element, for as Boyle stated, the particles of two sets of 
corpuscles might so regroup themselves that 'from the coalition 
there may emerge a new body, as really one, as either of the 
corpuscles was before they were mingled.' 1 Thus vinegar acting 
upon lead formed the "sugar" of lead (lead acetate) but by no 
means could the acid spirit of vinegar be recovered from the new 
compound; Boyle thought its corpuscles were destroyed. The 
indivisible corpuscles of glass were formed by a "coalition" of 
those of sand and ashes; so that resistance to chemical analysis by 
fire or acids was not a test of elementariness: for such indestructible 
corpuscles could as well be found in the bodies due to art, as in 
those due to nature. The same experience that taught Boyle that 
glass was not to be numbered among the elements, prevented him 
from knowing whether gold was one or not: he thought it was 
probably not. 

It is plain that Boyle's corpuscularian philosophy, in many ways 
so fertile, prevented him from taking any step towards the modern 
conception of the chemical element (an achievement usually 
credited to him). In fact it led in the opposite direction, for so 
long as Boyle, the physical chemist, concentrated on explanations 
of chemical reactions in terms of corpuscles and particles, he would 
be the less likely to believe that if elements existed at all, their 
existence was very significant to his new outlook. Lavoisier deter- 
mined that if a body resisted chemical analysis it should be 
accepted, pragmatically, as an element. Boyle could not have 
done this, because he thought in corpuscular terms. No body made 
up of corpuscles could be simple, homogeneous or elementary in 
the strict sense, because the corpuscles themselves were com- 
pounded of a variety of particles. The pragmatic test of resistance 
to analysis proved only that some concretions of these particles 
into corpuscles were more coherent than others, whether brought 
about by nature (gold) or by art (glass). But coherence and 
elementariness could not be equivalent, since Boyle knew that 
1 Works (London, 1772), vol. I, pp. 474-5, 506-7. 


some corpuscles whose coherence resisted analysis were factitious, 
i.e. non-elementary. 

The impasse was complete, and Boyle could not avoid it. Nor 
was it really important for him to do so: the truth that chemical 
changes occur by modifications of corpuscular structure, and by 
re-shuffling of the particles within corpuscles, was far more sig- 
nificant to him than a dubious search for primary elements, whose 
existence he was quite content to regard as hypothetical. In this 
he may be said to have anticipated the attitude of a modern 
physical chemist who (of course within a far more rich and 
exact conceptual framework) thinks in terms of molecules, atoms, 
ions and kinetic theory, without paying much attention to the 
elementariness of hydrogen or carbon. 

That Boyle's chemical theory was predominantly shaped by his 
corpuscularian physics is apparent from many works beside the 
Sceptical Chymist. He was no dogmatist, he was no follower of 
systems, he believed that hypotheses should be framed to fit the 
facts, but it was quite clear to him that complete scepticism and 
abhorrence of all theory were antithetical to true philosophy. 1 
Indeed, his ambition to bring chemistry into natural philosophy 
would have been meaningless had he not had a theory of natural 
philosophy, essentially a theory of matter, to hand for the purpose: 

I hoped I might at least do no unseasonable piece of service to the 
corpuscular philosophers, by illustrating some of their notions with 
sensible experiments, and manifesting, that the things by me treated 
of may be at least plausibly explicated without having recourse to 
inexplicable forms, real qualities, the four peripatetick elements, or 
so much as the three chymical principles. 2 

Thus for Boyle solution always represented the intcrspersion of 
the corpuscles of the solvent among those of the dissolved body, 
heat consisted of material particles, and "air" of all kinds mainly 
of elastic corpuscles of a particular type, among which the 
mingling of other corpuscles gave each "air" its own character. 
He constantly attributed the properties of acids, oils, salts, etc. 
to the nature of their component corpuscles. In fact the theory was 
brought into play whenever Boyle commented on a chemical 
experiment. Instances are particularly numerous in the Origin of 
Forms and Qualities, where (as examples chosen at random) he 

1 Cf. Ibid., p. 591. 

2 Certain Physiological Essays (1661), Works, vol. I, p. 356. 


spoke of 'the body of silver, by the convenient interposition of 
some saline particles [being] reduced into crystals ' of Luna cornea 
(silver chloride); or, of another experiment, 'considered that the 
nitrous corpuscles [of nitric acid], lodging themselves in the little 
spaces deserted by the saline corpuscles of the sea-salt, that passed 
over into the receiver, had afforded this alkali 5 ; 1 or again declared 

the more noble corpuscles which qualify gold to look yellow, [and 
to resist nitric acid] . . . may either have their texture destroyed 
by a very piercing menstruum, or, by a greater congruity with its 
corpuscles, than [with] those of the remaining part of the gold, may 
stick closer to the former and ... be extricated. 2 

Corpuscularian ideas were especially developed by English 
scientists in relation to the allied reactions of combustion and 
calcination. Both were anciently regarded as separations: the 
ash or calx (oxide) remaining was an earthy residue left after the 
more volatile parts of the combustible or metal had been driven 
off by fire. It was well known, however, that the calx (oxide) 
exceeded the original metal in weight: whence Jean Rey was led 
to believe (in 1630) that though the calx was lighter than the 
metal in nature, it became heavier by the attachment to it of air 
which had become thickened in the furnace. Boyle later thought 
that the increased weight came from fire-particles penetrating 
the walls of the crucible and impregnating the calx. This explana- 
tion was widely accepted until it was decisively confuted by 
Lavoisier. With regard to combustion it was well known to Boyle 
and others that bodies would not burn without air, unless (like 
gunpowder) they contained some nitrous material. A familiar 
experiment (originally described by van Helmont) showed that 
when a candle was burnt in a closed vessel over water, the air 
within diminished and the water rose up inside. From these and 
other observations Robert Hooke sketched a theory in Micrographia 
according to which combustible bodies were dissolved by a certain 
substance present in the atmosphere, this solution (like others) 
evolving great heat, and thus flames, which Hooke took to be 
' nothing else but a mixture of Air, and volatil sulphureous parts 
of dissoluble or combustible bodies, which are acting upon each 

1 i.e., KC1 + HNO 3 = KNO 3 + HC1. 

2 Origin of Forms and Qualities, Section VII. Boyle is obviously far from 
thinking that gold might consist of a single kind of corpuscle. 


other.' This aerial substance he identified with 'that which is 
fixt in Salt-peter* This same theory was elaborated in much greater 
detail by the physician John Mayow in 1674, who also set it 
uncompromisingly in the corpuscularian framework. In his view 
the atmosphere consisted of a mass of air-corpuscles with which 
were mingled others that he called " nitro-aerial particles," 
because they were fixed in nitre and nitric acid. These nitro-aerial 
particles were highly elastic, and responsible for the hardness of 
quenched steel. They also corroded metals exposed to the air. 
The same particles, reacting violently with the sulphureous 
corpuscles of combustible bodies, produced heat and flame, as 
Hooke had said; therefore combustion could not occur without 
them. Air in which combustion had taken place was (in some 
way which Mayow did not explain) deprived of its nitro-aerial 
particles, thereby decreasing in elasticity and causing the water 
to rise in van Helmont's experiment. Similarly air breathed by 
animals lost its nitro-aerial particles, so that the expired air was 
less elastic (i.e. occupied a smaller volume) than that inspired; 
the same particles caused the blood to ferment and provoked 
animal-heat. They caused fermentation generally; they formed 
the fiery body of the sun, and the flash of lightning; in short, the 
nitro-aerial particle became in the hands of Mayow a deus ex 
machina for explaining many totally unrelated phenomena. He 
had no idea that these particles made an "air," or that the 
atmosphere was a mixture of "airs" of which that was one. The 
notion (first put about by Thomas Beddoes, Davy's patron) that 
Mayow had closely anticipated the oxygen-theory of Lavoisier 
cannot support serious examination: his was a typical corpuscul- 
arian philosophy. 

During the next hundred years studies on combustion and 
calcination were to prove vital to the progress of chemical theory, 
while the accumulation of empirical fact was proceeding in a way 
which rendered the dubiety of theory almost irrelevant. The 
attempt to explain chemical reactions in terms of the mechanistic 
theory of matter, begun by Descartes and continued by Boyle, 
Mayow and others, was abandoned in the early years of the 
eighteenth century. Its claims were too wide, its achievements too 
lacking in definition. Not that chemists doubted the particulate 
structure of matter, but since nothing was known about the size, 
hardness, shape, etc. of corpuscles, statements in which these 


properties of the fundamental constituents of matter were involved 
were recognized as meaningless. This downfall of Boyle's hopes 
the cause of the subsequent neglect of the theoretical import in 
his writings was accelerated by the ascendancy of Newtonian 
mechanics. The laws which governed the stars must be applicable 
also to the smallest particles of matter, and the laws of chemical 
affinity be subject to the supreme law of gravitational attraction. 
The elements of this theory, already sketched by Newton in the 
Queries to his Opticks (I7O4), 1 were soon after worked out more 
completely by Kcill and Freind. The later empirical study of 
affinity (e.g. by Geoffrey, who published tables of affinity in 1718) 
was certainly encouraged thereby, but after the middle of the 
century (when attraction had long been abandoned by practical 
chemists) it became clear that the property of attraction in 
corpuscles was as intangible as their other properties: nothing 
could be said about it, other than that it existed. And so the am- 
bition to render chemistry a branch of physics was, for the time, 
frustrated. Dalton's atomic theory was conceived entirely in a 
chemical context, and it was under the aegis of chemistry that the 
second penetration of atomism into modern scientific thought was 
to take place. 

If to many chemists of the early eighteenth century it seemed 
hopeless to base their theories directly on the properties of atoms 
or corpuscles, they were not the less convinced of the existence of 
elements or principles of an ultimately corpuscular nature. The 
principles adopted by the German chemist G. E. Stahl (1660 
1734) from the writings of J. J. Becher (whose Physica Subtenant 
of 1669 Stahl republishcd in 1703) were accepted by most of his 
colleagues, especially those in Germany and England, until near 
the close of the century. Stahl's principles were water and three 
kinds of earth: air was not chemically active. The three earths 
corresponded to the three principles of the iatrochemists, but 
Stahl preferred to call the second (sulphur) phlogiston. The 
followers of Stahl made much use of affinity in explaining reactions 
(meaning, in this case, the tendency of like to react with like) 2 

1 Newton's investigations into chemistry were almost completely unknown 
in detail at this time, as indeed they still are. 

2 Thus Junker on the formation of corrosive sublimate (Helene Metzger, 
Newton, Stahl, Boerhaave et la Doctrine Chimique (Paris, 1930), p. $42): * Common 
salt consists of an acid and an alkaline base. Vitriolic acid, being more powerful, 
seizes the base and drives out the acid from the salt. This acid would escape 


and of a novel theory of salts (as earth + water). The theory of 
phlogiston was far from being the whole of their chemical doctrine, 
though it was the dominant feature of that doctrine because it 
permitted the co-ordination of many previously isolated facts. 1 
Phlogiston was the substance emitted during combustion and the 
calcination of metals, the "food of fire" or "inflammable prin- 
ciple." The complete, or almost complete, combustion of charcoal, 
sulphur, phosphorus, etc. demonstrated that these bodies were 
very rich in phlogiston: while the formation of sulphuric acid, 
phosphoric acid, etc. from the solution of the fumes produced by 
combustion demonstrated that the substances themselves actually 
consisted of nothing but the acid joined to phlogiston (i.e. sulphur 
minus phlogiston > sulphuric acid: therefore sulphuric acid + 
phlogiston = sulphur) . When a metal was heated, the phlogiston 
driven off left a calx behind (therefore calx -f phlogiston= metal). 
Conversely, by heating the calx with charcoal, phlogiston was 
exchanged and the metal restored. Many reactions became 
comprehensible when interpreted in terms of an exchange of 
phlogiston, so that often where a modern chemist sees a gain or 
loss of oxygen, Stahl saw an inverse loss or gain of phlogiston. 

Oxygen has weight: and a modern chemist would insist that 
phlogiston ought to have negative weight, a suggestion actually 
mooted when Stahlian chemistry was already moribund. The 
matter was not serious at first. Boyle himself had explained the 
increased weight of a calx in a way that nowhere conflicted with 
the idea of phlogiston. Until such time as gases were collected, 
and the gain or loss of weight due to the participation of a gaseous 
element in a reaction could be correctly estimated by means of 
the balance, it was impossible to achieve a balance of masses in a 
chemical equation. Chemical mathematics, before 1775, was such 
that there was no palpable absurdity in the conception of 
phlogiston as a material fluid: as Watson said, 

You do not surely expect that chemistry should be able to present you 
with a handful of phlogiston, separated from an inflammable body; 
you may just as reasonably demand a handful of magnetism, gravity, 

freely, but meeting with another substance (mercury) with which it has some 
analogy (though not so great as with its own base), it forms a saline substance 
with it. This substance (corrosive sublimate) is volatile because both mercury 
and the acid from salt are volatile: they have an identity of "mercurial 

1 This is particularly emphasized by Mme. Metzger, op. cit. 


or electricity. . . . There are powers in nature which cannot otherwise 
become the objects of sense, than by the effects they produce; and of 
this kind is phlogiston. 1 

The purely logical objection which has often been raised against 
the phlogiston theory is therefore of small value. Eighteenth- 
century scientists readily admitted the existence of weightless, 
impalpable fluids such as electricity and caloric. Caloric was 
indeed phlogiston revived, stripped of its chemical attributes to 
become Lavoisier's "pure matter of heat." 2 Nor did Stahl's 
influence check the progress of chemistry as an empirical science; 
rather his views provided a useful provisional scheme for the 
explanation of many experiments. As such many chemists accepted 
them, without sacrificing their liberty to interpret experiments in 
the light of the evidence alone. Lavoisier himself was at first far 
more keenly aware of the need to scrutinize experimental data, 
than of any implausibility inherent in the phlogistic doctrine 
itself. The practical chemists were always far more interested in 
particular problems than in universal theories; some, like Boer- 
haave, were never followers of Stahl. Hence it seems unnecessary 
to suppose that the fortunes of chemistry were inextricably bound 
up with those of the phlogiston theory, whose scope was largely 
restricted to the phenomena of combustion and calcination; but 
it is certain that the age of phlogiston witnessed great progress in 
chemical experimentation, though the hypothesis has so often been 
characterized as futile and retrogressive. In the phlogiston period 
the chemistry of gases was begun by Black, Cavendish, Scheele 
and Priestley; the vain attempt to base chemical theories on 
organic and inorganic reactions conjointly was abandoned; there 
were striking improvements in the analysis of inorganic com- 
pounds. Considerable development in the application of chemistry 
to manufacture also took place. By contrast, few comparable 
discoveries can be linked with the corpuscular chemistry of Boyle 
and Mayow. 

Irrespective of its ultimate redundancy, phlogiston was un- 
doubtedly a useful concept until about 1 765, when the systematic 

1 Richard Watson: Chemical Essays > vol. I (London, 1782), p. 167. 

2 Compare Watson on phlogiston: * Chemists are of opinion that fire enters 
into the composition of all vegetables and animals, and most minerals; and 
in that condensed, compacted, fixed state, it has been denominated the 
phlogiston.' (Op. cit. 9 p. 165.) 


study of gases was begun by Henry Cavendish (1731-1810). It 
enabled a consistent interpretation to be given to experiments on 
combustion, and many others involving oxidation and reduction. 1 
Chemists gained a valuable insight into a number of reactions in 
phlogistic terms, and so learnt to treat natural substances 
sulphur, carbon, salts, alkalis, acids, metals, earths, and so forth 
as the really active participants in their processes. Lavoisier's 
chemical revolution was based on a level of factual knowledge, 
and a pragmatism with regard to chemical combination, un- 
equalled at any earlier time. The fact that it often happened that 
Lavoisier could simply invert the phlogistic doctrine is evidence 
of the service which the phlogistonists had performed. Only with 
the discovery of the common gases when hydrogen was taken to 
be pure phlogiston, nitrogen to be phlogisticated air, oxygen to 
be dephlogisticated air, etc. did phlogiston become a serious 
impediment to the interpretation of experimental work; only then 
did the question of its usefulness as a hypothesis become really 

The technique of collecting gases over water was invented by 
Stephen Hales before 1720; Joseph Priestley (1733-1804) substi- 
tuted mercury when working on water-soluble gases. Hales 
examined "airs" produced in a variety of chemical processes, 
particularly in order to discover the quantity evolved from a given 
weight of materials, but he drew no new qualitative distinctions 
between them. From his experiments he concluded that "air" 
was capable of being fixed in substances as a solid. The first 
chemist to label such a "fixed air" decisively, at the same time 
discovering its function in a number of reactions, was Joseph Black 
(1728-99). The linkage is important, for many "airs" had been 

1 It is not difficult to find examples of reasoning in phlogistic terms which 
led to satisfactory experimental procedures. Thus Scheele (1779) wished to 
establish the ratio by volume of "pure air" (oxygen) to "foul air" (nitrogen) 
in the atmosphere. He argued: 'When this pure air meets phlogiston uncom- 
bined, it unites with it, leaves the foul air, and disappears, if I may say so, 
before our eyes. If, therefore, a given quantity of atmospheric air be included 
in a vessel, and meet there with some loosely adhering phlogiston, it will at 
once appear, from the quantity of foul air remaining, how much pure air was 
contained in it before.' He therefore took a small amount of iron filings, mixed 
with sulphur and a little water, which he knew to be a preparation very rich 
in phlogiston, and used it to effect the "disappearance" of the "pure air" in 
a known volume of common air. Scheele's mixture does in fact take up oxygen 
very readily. The result he obtained (9 : 24) was not good, but his procedure 
was perfectly correct. (Cf. Chemical Essays (London, 1901), pp. 190-4.) 


roughly identified in the past (e.g. as inflammable, or extinguish- 
ing flame), but none had been clearly described as being distinct 
in species from common air, nor had any function been ascribed 
to them as participants in chemical processes. The most striking 
part of Black's work (Experiments upon Magnesia alba, etc., 1 756) 
was his proof that quicklime was lime deprived of "fixed air": the 
quantitative relation was completely established. Black found that 
a mild alkali became caustic through loss of its "fixed air," and 
that "fixed air" was emitted with effervescence when lime was 
dissolved in acids. He made constant use of the concept of affinity 
in explaining his experiments: thus, discovering that when quick- 
lime was added to a mild alkali, the original weight of lime 1 was 
precipitated and the alkali rendered caustic, he said that "fixed 
air" had been exchanged because of its greater affinity for quick- 
lime than for the alkali. He carefully pointed out that though 
both water and the atmosphere contained "fixed air," it was not 
identical with "common air." Later he discovered it in exhaled 
breath, and in common air passed over burning charcoal: the 
precipitation of lime from lime-water proved to be a specific test. 
The whole essay was a neat model of scientific method: at one 
stage in his work Black drew up a list of predictions, each of which 
he was able to verify by experiment, thus proving that "fixed air" 
played the part he had assigned to it. 

In all this there was no mention of phlogiston. Though Black 
was very far from rejecting the phlogiston theory in its entirety 
until long after this time, he was convinced that his experi- 
ments could be explained without phlogiston, and he resisted all 
attempts to argue that phlogiston was involved in them. Black 
had not, in 1756, actually collected his "fixed air," for the tech- 
nique of imprisoning fugitive "elastic fluids" in vessels was still 
almost unknown to chemists. It was described by Cavendish in 
his paper On factitious airs (1766), and thereafter widely used. He 
distinguished between Black's "fixed air" and another (hydrogen) 
deriving (as he thought) from metals, which he found to be lighter 
than common air. At about the same time the German apothecary 
Carl Wilhelm Scheele (1742-86) separated the two major con- 
stituents of the atmosphere "Feuerluft" (oxygen) and "verdor- 
bene Luft" (nitrogen): he also prepared oxygen in various ways 
in the laboratory, as did Joseph Priestley, quite independently, in 
1 Calcined by Black to make the quicklime. 


1774. Most of the characteristic qualities of these and other gases 
were noted. 

Such were the strategic few, among a great number of other 
major discoveries made by chemists who thought without reserva- 
tions in the framework of which phlogiston was an essential part. 
Two of the pioneers of gas chemistry, Priestley and Cavendish, 
were never reconciled to Lavoisier's doctrines. Their refusal was 
no doubt due to rigidity of mind, but it points also to the fact that 
the phlogistic theory had imposed no barrier upon the activities 
of these skilful experimenters. It also emphasizes Lavoisier's own 
originality in devising new interpretations of their experiments. 
While the adherents of phlogiston were by no means agreed in 
the details of their exposition Priestley, for example, thinking 
of oxygen as dephlogisticated air, and Cavendish preferring to 
treat the gas as dephlogisticated water a situation by no means 
unusual on the frontier of research, these hesitations did not 
inhibit inquiry; on the contrary, it is quite clear that Scheele, 
Priestley and Cavendish were each at times induced to make 
certain fertile experiments by reasoning in the phlogistic manner. 

The situation in which the further progress of a branch of 
science is directly dependent upon an adequate matching of 
theoretical concepts and experimental facts is by no means 
uncommon. This was certainly the case when Galileo and Newton, 
respectively, revised the concepts of mechanics, and again with 
physics in the nineteenth century. But though such a matching of 
fact and theory is always useful it is far from being invariably 
essential. Did such a situation exist in chemistry at the end of the 
eighteenth century? The evidence would seem to suggest that it 
did not. The empirical attitude of the great experimenters was in 
reality far more important than their theorization: it is therefore 
the less likely that any plausible modification of the doctrines 
prevailing through the first three-quarters of the eighteenth 
century would have had much influence on the course of events. 
No one would deny that Lavoisier was the first chemical theorist 
of genius. No one would deny that his interpretation of the 
phenomena was far superior to that of the phlogiston theory: it 
was one upon which the ultimate advancement of chemical 
knowledge depended. Yet it is also perfectly clear that the 
inventive empiricism of his contemporaries was just as necessary 
for this as his own logical, interpretative intellect, and that, 


moreover, the rapid progress of chemistry in the nineteenth 
century owed a great deal to developments, such as electro- 
chemistry and the atomic theory, to both of which Lavoisier's own 
insight into the nature of chemical reactions contributed nothing. 
Antoine Laurent Lavoisier (1743-94) was, like Newton, less 
the author of new experiments than the first to realize their full 
significance. Experimentation for its own sake, which delighted 
Priestley, had little appeal for him. In his laboratory work he 
proved himself a skilful analyst, and an able exponent of the 
quantitative methods of Black and Cavendish, but not greatly 
imaginative in the way that Cavendish (or, later, Faraday) was a 
supremely imaginative experimenter. None of his most famous 
experiments was new: the element of originality in them was 
limited to Lavoisier's insistence upon paying heed to the teachings 
of the balance: 

We may lay it down as an incontestable axiom, that, in all the opera- 
tions of art and nature, nothing is created; an equal quantity of 
matter exists both before and after the experiment; the quality and 
quantity of the elements remain precisely the same; and nothing 
takes place beyond changes and modifications in the combination of 
these elements. 1 

His first investigation was into the composition of the water in 
various localities about Paris. In his second he refuted the ancient 
fallacy that water was converted into earth by long heating and 
evaporation: he found that the " earth" obtained was dissolved 
glass. Thirdly, he discovered that air was " fixed" in phosphorus 
pentoxide and sulphur dioxide (made by burning phosphorus and 
sulphur), bringing about an increase of weight. He predicted that 
the same would be found true of all combustibles, and that the 
increased weight of metallic calces was due to a similar fixation of 
air. This last prediction he confirmed (1772), by reducing lead 
oxide to lead with charcoal: a large quantity of air was evolved. 

Lavoisier had set out to produce facts, and by quantitative 
methods he had succeeded. Some of them were not exactly new, 
though they had formerly been less precisely stated, but he per- 
ceived that there was enough to make the phenomena of combustion 

1 Elements of Chemistry (trans, by Robert Kerr), (Edinburgh, 1790), p. 130. 
But Lavoisier was in no sense the first chemist to subject notions of chemical 
composition to quantitative tests. There are many earlier examples of this 


and calcination worthy of detailed examination. All his future 
success followed from his apprehension of this significance. He 
embarked upon ' an immense series of experiments ' intended to 
reveal the properties of the different "airs" involved in chemical 
reactions, which seemed ' destined to bring about a revolution in 
physics and chemistry. 5 In fact, however, Lavoisier's qualitative 
study of gases did not advance very far between February 1773 
(when he wrote the note just quoted) and October 1774, though 
he did satisfy himself that the "air" given off in the reduction of 
lead oxide with charcoal was Black's fixed air, and that Boyle's 
explanation of the origin of the increased weight of metallic calces 
was false. 1 At this stage he was still uncertain whether the "air" 
combining with metals to form their calces was Black's fixed air, 
or common air, or something occurring in the atmosphere. He 
had, apparently, missed the importance of Black's own observa- 
tion that burning charcoal was a source of his fixed air. He could 
hardly have claimed, at this point, to have done more than 
indicate a series of reactions in which some kind of air was 
involved, parallel to those already described, more completely, 
by Black. 

In October 1774 Lavoisier was informed by Priestley himself of 
the evolution of an "air" (oxygen) from the red calx of mercury 
(mercuric oxide) when reduced by itself to the metal with the aid 
of a strong heat. 2 Some months later Priestley had established that 
this " dephlogisticated air" (as he now called it) was respirable as 
well as capable of supporting combustion. Soon after Lavoisier 
was able to report new experiments to the Academic des Sciences: 
the calx of mercury reduced with charcoal gave fixed air, reduced 
alone it gave off Priestley's new air. Therefore it was, said 
Lavoisier, common air in a highly active state which combined 
with metals to form their calces. Evidently he did not yet regard 
it as a particular constituent of the atmosphere, a view which he 
adopted in the course of the next two years, when he realized that 
one fraction of the air was inert during combustion and calcina- 
tion. This he called mofette. The atmosphere, therefore, contained 
two "elastic fluids," as Scheele had discovered some time before. 

1 In this he had been anticipated by the Italian chemist, Beccaria. The 
equivalence of the increased weight of the calx with the weight of the air 
admitted when the retort was opened was not as exact as Lavoisier wished. 

8 Lavoisier's own claim to the discovery of oxygen is generally rejected. 


By August 1778 Lavoisier could announce that "eminently 
respirable air" (the "dephlogisticated air" of Priestley) combin- 
ing with a metal, formed a calx, and that the same air combining 
with charcoal gave Black's fixed air (carbon dioxide). The prob- 
lem of calcination was thus solved, and other discoveries followed 
rapidly. Lavoisier found that sulphur and phosphorus, in burning, 
also combined with "eminently respirable air" only, and that it 
was this combination that yielded acids by solution in water. He 
found the same air in nitric acid, and was led to conclude that it 
was present in all acids. In respiration, the mofette part was exhaled 
unchanged, but the respirable part was exhaled as the fixed air 
which Black had found in the breath. From experiments carried 
out in collaboration between 1 782 and 1 784 Laplace and Lavoisier 
judged that respiration was a process of slow combustion, for the 
amount of heat produced by an animal in breathing out a certain 
volume of fixed air, was almost equal to the amount produced in 
burning enough charcoal to give the same volume. 

In his memoirs before 1778 Lavoisier had not eschewed the 
word "phlogiston" completely, though he was uncertain of its 
role in his experiments, if it existed at all. By 1778 the elements of 
his new theory of oxidation were quite firm, and in it phlogiston 
had no part for he had proved that the phlogiston-concept was 
the inverse of the truth. The processes of oxidation (combustion, 
calcination) were not analyses but syntheses, in which phlogiston 
was as redundant as it was in Black's fixed-air reactions. Once 
the pattern of the substitution of the oxygen-concept for the 
phlogiston-concept became clear, it could be extended to whole 
groups of reactions, over almost the whole area of chemistry, by 
the development of suitable analogies. Indeed it was possible to be 
deceived by such analogies. 1 Proceeding in this way, it became 
ever more plausible to propose the exclusion of phlogiston from 

1 e.g. in Lavoisier's account of the relation of "oxygenated muriatic acid" 
(chlorine) to "muriatic acid*' (hydrochloric). Lavoisier was convinced that 
the latter was a compound of an unknown base with oxygen (as were all acids, 
in his view), and the former a compound of the same base with a higher 
proportion of oxygen (by analogy with sulphurous, sulphuric acids, etc.). 
Therefore he postulated aXO + . . . O 2 -> 2XO 2 + ... for 4.HC1 -f- . . . O a 
-> C1 2 -f- 2H 2 O + . . . His name for it was simply the inverse of "dephlogisti- 
cated marine acid gas" (Scheele) and really considerably less appropriate, 
since if hydrogen = phlogiston (Cavendish), HG1 H -> Gl. (Cf. Elements of 
Chemistry, pp. 69-73, 2 33~5)* Davy discovered the true composition of HG1, 
and established that chlorine is an element. 


the doctrine of chemistry altogether. In 1783 Lavoisier was 
impelled to make a direct attack upon the phlogiston theory, 
which he seems to have disliked even before he had any very solid 
grounds for doing so. In this comparison of his own theory with 
that of the phlogistonists, he insisted upon their inconsistencies 
and duplications of hypothesis much as Galileo had analysed the 
weaknesses of his opponents long before. Phlogiston was not 
merely superfluous; it had come to mean quite different things in 
different contexts, and had become a mere drudge in chemical 

From this time the number of adherents to Lavoisier's views 
increased steadily, first in France, and then abroad. One serious 
difficulty remained. Lavoisier had not been able to discover the 
product of burning " inflammable air" (hydrogen) with common 
air, or with "respirable air" (oxygen). Nor could he account for 
the evolution of hydrogen when metals were dissolved in weak 
acids, and its non-appearance when the calces of metals were so 
dissolved. All this could easily be explained in terms of phlogiston. 
Once again enlightenment came from the English experimenters. 
In 1 782 Cavendish continued experiments begun by Priestley and 
others in which an electric spark was passed through mixtures of 
hydrogen and common air. The work was done with wonderful 
neatness, and he was able to identify the condensate inside his 
glass vessel as common water, the gases disappearing in a ratio of 
2:1 by volume. By June 1783 these experiments were known to 
Lavoisier, who, paying Cavendish scant tribute, hastily repeated 
them. Initial scepticism was replaced by a rapid reinterpretation 
in terms of his theory: water was the oxide of hydrogen, and 
hydrogen was evolved by the action of metals from the water 
present in the weak acids. 

The last act in the "chemical revolution" was the establish- 
ment of a new terminology. The existing names of compounds 
were either misleadingly descriptive ("butter of antimony"), or 
redolent of the displaced theory ("dephlogisticated air") and 
even older notions ("spirit of salt"), or based on common words 
like "salt" and "earth." In 1787 Lavoisier and three of his 
French adherents devised a new nomenclature, still substantially 
preserved, in which the names were intended to identify the 
nature of the substances. Thus hydrogen (water-former) replaced 
"inflammable air" and oxygen (acid-former) "eminently respirable 


air." Mofette became azote (inert) or to non-French chemists 
nitrogen (nitre-forming). Compounds of an element with oxygen 
were all oxides, with sulphur sulphides, etc. This aim to establish 
regular patterns of nomenclature has been consistently followed. 
At the same time Lavoisier abandoned the attempt to seek (in 
chemistry) any reality more fundamental than that revealed by 
ordinary analysis. Substances which resisted analysis were, to him, 
elements; for example the common gases, metals, sulphur, carbon, 
lime, and a number of earths and other "radicals" some of which 
were soon analysed into other constituent elements. Lavoisier 
already used the word " radical" in the sense of a unit in chemical 
reactions, and an element was simply an indestructible radical. 
All this was fully explained in the first textbook of the new 
chemistry, the Traiti Elementaire de Chimie of 1 789. 

Its publication draws a convenient line of demarcation. Yet it 
is important to recognize how little, as well as how much, was 
really new in it. The theory, and the arrangement based upon the 
theory of chemical combination, was all Lavoisier's. The inorganic 
experiments and substances described had almost all been known 
for twenty years, and the majority for much longer. Lavoisier and 
his friends, however, had created the organic section (dealing 
with the composition of alcohol and sugar, etc.) almost unaided. 
If the table of elements was new, it derived (by a simple modifica- 
tion) from the older chemists' practical habit of treating phos- 
phorus, sulphur, metals, etc. as virtually compounds of element 
+ phlogiston. Lavoisier still spoke of earths and alkalis much as 
they had done, and knew little more about them. On the mystery 
of chemical affinity he said nothing, on the plea that it was unsatis- 
factory to discuss it in an elementary treatise. Perhaps it is most 
surprising, in the beginnings of modern chemistry, to discover 
Light and Heat listed as elements. 'Light,' wrote Lavoisier, 
* appears to have a great affinity with oxygen , . . and contributes 
along with caloric to change it into the state of gas.' It also com- 
bined with the parts of vegetables to produce their green pigment. 1 
Lavoisier also regarded light as a modified caloric, or vice versa; 
this caloric, the invisible, weightless matter of heat was essential 
to his view of matter. Caloric was interspersed between the 
particles of bodies: in small measure in the solid, to a great extent 
in the liquid, and most of all in the gaseous state when (so to 

1 Elements of Chemistry (trans, by Robert Kerr), (Edinburgh, 1790), p. 183. 


speak) the particles of matter floated freely in the fluid. Oxygen 
gas was really oxygen matter plus caloric, which was liberated as 
free heat when the oxygen became "fixed" in combination with 
a combustible. Caloric also caused the physical expansion of 
heated bodies, by pushing their particles farther apart. Here are 
undoubted vestiges of corpuscular mechanism in Lavoisier's 
thought, when he handled (in a method which would have been 
familiar to Boyle, but unacceptable to him) the problem of the 
origin of heat and flame, which had so much puzzled Boyle 
himself. Here, on the boundary of physics and chemistry, the 
ideas of the seventeenth-century physico-chemical corpuscularians 
still survived. 

What Lavoisier did is clear enough: how was he able to do it? 
Disregarding the noisy disputes of theorists and rival interpreta- 
tions of this or that experiment, factors can be discerned beneath 
the surface, not always conspicuous to the great theorist himself, 
leading towards the chemical revolution. Some are fairly obvious: 
for example, increased reliance on quantitative procedures. What 
was important here was not the mere tabulation of weights and 
measures, still less the making of a serious mistake like Boyle's 
(p. 324) for numerous exposures of the error failed to make plain 
its momentous importance but rather use of measure for con- 
structive purposes, to arouse or to answer questions. "Let us 
regard the facts without prejudice" said Lavoisier; but a table of 
facts concerning quantitative reactions is not, and can never be, a 
chemical theory. He might rather have said "Let us be astonished 
when we contrast the facts with the expectations created by our 
theory." This was the spirit of Galileo's, of Newton's, of Black's 
researches. Rigorous quantitative methods were only useful in 
proportion as they brought about a sharper juxtaposition of fact 
and theory, of the flint and steel to which Lavoisier supplied the 

In the second place, the work of the great theorist co-ordinated 
that of the great experimenters in more senses than one. They 
supplied him with the pieces whose interlocking provided a perfect 
picture, and they also built the framework of chemical knowledge 
within which alone his theory could carry conviction. If Lavoisier's 
prime experiments were rarely of his own invention, they were 
the more telling in that they were familiar, in the same way that 
Galileo's reasoning was the more forceful because it was focussed 



on commonplace experiences. As a third example, it may be 
observed that Lavoisier extended to its logical conclusion a 
practical, pragmatic way of thinking about the matter in a 
chemist's retort which went back at least to the mid-seventeenth 
century. Earlier chemists had thought of a salt as a metal-stuff 
and an acid-stuff in combination, had carried out analyses in 
terms of the sulphur-content, metal-content, alkali-content and 
so forth of the original material, and having come to see chemical 
reactions as a process of subtraction and addition, they had 
invented the theory of affinity to account for it. To this chemist's 
attitude to matter and its transformations ignoring the question 
of the ultimate physical reality of what took place Lavoisier 
brought rigour and precision, but it can hardly be said that he 
created it. Perhaps in this was the core of the chemical revolution, 
that it severed chemistry from physics, albeit temporarily. Boyle 
had been frustrated because he tried to explain chemical pheno- 
mena rigidly in terms of a physical theory, consciously denying 
himself the use of any other concepts; Lavoisier succeeded most 
where he was the pragmatic chemist, least when (in his theory of 
caloric) he in turn sought to bind physics and chemistry prema- 
turely in one. Despite electro-chemistry and other developments 
of the first half of the nineteenth century, this hiatus continued, 
lasting throughout the formative period of modern chemistry. 
Only in the third stage of chemical atomism, with the acceptance 
of Avogadro's hypothesis after 1869 and the publication of the 
periodic table did the reconciliation of chemistry and physics, 
foreseen by Boyle, and partially abandoned by Lavoisier, become 
an attainable objective. 



THE dual character of eighteenth-century science has already 
been remarked upon. On the one hand, those threads which 
the historian of science has carefully followed through the 
preceding hundred years tend to become dry and brittle; the ex- 
citement had passed and there remained but its sequelae, a rather 
timid experimentation and a cool, logical extension of what were 
now commonplace ideas. The mood changed too. The rebellious 
spirit of a Galileo was no longer necessary, for the works of Aris- 
totle had passed out of serious science into the care of classical 
scholars, and the scientific revolutionaries were now respectable 
citizens of the republic of learning. As the scientific movement 
became more comme ilfaut, so it acquired an element of dullness: 
no one can be very interested in the sort of chemical experiments 
that Dr. Johnson performed to soothe his mind, in the lessons on 
mechanics that were arranged for the royal children, or in the 
scientific pot-boilers of John Wesley. As science became fashion- 
able, patronage demanded that a major discovery be presented as 
a humble tribute rather than as a challenge to established philo- 
sophy. But these idiosyncrasies of a society which left Priestley 
to the mercy of the Birmingham rabble and made Banks President 
of the Royal Society, and in which the Ladies* Diary was filled with 
mathematical conundrums, are not after all of the first importance. 
Nor was the England of Hume and Gibbon or the France of 
Voltaire and Diderot immune to the challenge of intellect; and it 
is obvious from what has gone before that in its science the 
eighteenth century was by no means an age of mere continuations, 
for the creative drive was not so much weakened as altered in 

On the other hand, therefore, new threads of rich interest 
strengthened the texture of science in the eighteenth century. 
Strategic advances were not made along the broadest paths, but 



where the giants of the seventeenth century had been least suc- 
cessful. This is strikingly apparent in physics. The natural heirs 
of Newton were among the French school of mathematicians 
D'Alembert, Clairaut, Lagrange, Laplace. The fundamental con- 
cepts of mechanics were defined more neatly and exactly by them, 
while at the same time they moulded the mathematical structure 
of the science into a beautifully complete and harmonious series of 
equations. They achieved an elegance and precision in compari- 
son with which the work of the seventeenth century seems involved 
and fumbling: even Newton's Principia, beside the Mtcanique 
Celeste of Laplace, reveals a clumsy mathematical treatment. And 
Laplace, unlike Newton, saw no reason to bring God into his 
hypotheses. But the refinements of the French mathematicians 
in no way modified the essential principles of mechanics, which 
were already fixed, although their more penetrating analysis en- 
abled some new problems to be solved, and some old errors to be 
corrected. The many new and useful ideas that they put forward 
must therefore be ascribed to the second order of discovery, as 
being derivative rather than fundamental. At the same time, at a 
lower level, experimentation in mechanics, pneumatics, hydraulics 
and optics the organized departments of physical science was 
taken up extensively. In Leiden Musschenbroek, in London the 
Hawksbees, were already creating before 1710 a tradition of 
demonstrative teaching. It is perhaps invidious to call their lec- 
tures semi-popular, for the experiments they devised were often 
far more ingenious and conclusive than those suggested by the 
pioneer physicists. Such a work as Desagulier's Course of Experi- 
mental Philosophy (1734 etc.) was a valuable manual of laboratory 
practice and a sound introduction to physics without mathematics. 
Concurrently there was a steady improvement in the design of 
familiar instruments, such as the barometer, thermometer, hygro- 
meter, air-pump, balance and so on; with these multitudes of 
observations were performed, without, however, eliciting any 
major discovery. The situation in physics was clearly, so far as its 
more highly organized departments were concerned, very different 
from that in astronomy (for example), where Bradley's discovery 
of the aberration of light was the direct result of refinement in 
angular measure. Yet even so, problems of values arise, and it 
cannot be taken for granted that the less dramatic work of the 
eighteenth century had the less significance. It could be argued, 


for instance, that the graduated scales of Fahrenheit and Reaumur 
alone made thermometry effective in science, with important 
results in both physics and chemistry. 

It is indeed very easy to undervalue second-order discoveries 
in a period of consolidation. Creative ability of the first order is 
extremely rare, and though its works must figure largely in any 
short account of the development of science, it would be absurd to 
suppose that it could flourish apart from the context created by 
men with smaller endowments. Between the peaks of scientific 
achievement there is a time when activities are re-phased, when 
perspectives alter, when with an enlarged range of facts the major 
problems gradually modify their shape. Without this Newton 
could not have succeeded Galileo, nor Darwin Linnaeus. More- 
over, it very rarely happens that the statement or the demon- 
stration of a first-order discovery are so perfect that they win 
complete conviction, or that its potentialities are fully exploited. 
The task of welding the fabric of science together, of preserving 
the logic and homogeneity which originality in its highest 
degree often seems to imperil, usually falls to the derivative 
investigator, and it is by this consolidation, as well as by its most 
splendid feats of conceptualization and experiment, that science 

Two aspects of such consolidation are well illustrated in the 
experimental physics of the eighteenth century. The expedition 
to the head of the Gulf of Bothnia led by Maupertius and Clairaut 
in 1736-7 was a bold undertaking for the time. Forests tangled 
with fallen trees had to be penetrated, rapids navigated, and 
quadrants handled when the mercury had sunk far below zero, by 
these gentlemen fresh from the salons of Paris. Their purpose was 
to measure the length of a degree of latitude, in order to compare 
their result with that already obtained in France by Picard. Upon 
this comparison rested the verification of an important theory. For 
if the degree proved to be longer in northern than in southern 
latitudes, then the earth was flattened in the polar regions, as 
Newton had reasoned from dynamical considerations. This proved 
to be the case, and the ratio of the polar to the equatorial diameter 
of the earth was found to be 177/178. Some years later a similar 
ratio was worked out from the results of another geodetic expedi- 
tion to Peru (1735-43). The critics of the Newtonian theory of the 
earth's shape, including the astronomer Jacques Cassini, were 


thus decisively confuted. 1 Newton's theory, however, gave the 
ratio of flattening as 229/230. A much better agreement was 
obtained in Clairaut's own reinvestigation of the theory (1743), 
which yielded a formula relating the earth's ellipticity to the 
gravitational attraction at any latitude. 2 By these means, not only 
was the application of the principles of mechanics to the great 
mass of the earth itself validated, but the actual method of apply- 
ing them was improved to give a better coherence between theory 
and experiment. At the same time, new light was thrown on the 
pendulum experiments made in different parts of the globe. The 
impregnability of Newton's theory of attraction was further in- 
creased, at a time when it had still to win the confidence of many 
continental scientists. 

The course of these events was predictable. It was certain that 
if there was a controversy over the shape of the earth, it would be 
settled by making measurements that was the established spirit 
of the scientific revolution. It was also certain that if theory and 
measurement did not wholly coincide attempts would be made to 
re-examine the theory in search of some neglected factor. Exactly 
this happened and the theory was improved. In contrast, other 
second-order discoveries in eighteenth-century physics, though 
continuations of what had gone before, were altogether unpre- 
dictable. Perhaps the most striking of them was made by the 
London optician, John Dollond, in 1759. Newton had supposed 
that when a beam of light passed through a prism, the dispersion 
of the colours in the spectrum cast was in an invariable proportion 
to the degree of refraction, and quite independent of the material 
of the prism. Consequently he had held that chromatic aberration 
(caused by the failure of lenses to bring all colours to the same 
focus, owing to dispersion) was incapable of correction. The 
German mathematician Euler, thinking of the human eye as a 
perfect lens-system made up of several media, suggested that a 
triplet "lens" formed by enclosing water between the interior 
concave surfaces of two juxtaposed glass lenses would likewise be 
free from aberration. He was able to work out (1747) the required 
curvatures, but attempts to put his idea into practice failed. 

1 Cf. Pierre Brunet: La vie et Vcetwre de Clairaut, in Revue d'Histoire des Sciences , 
vol. IV (Paris, 1951), pp. 105-32. 

2 The theory was also revised a little earlier by the Scottish mathematician 
Maclaurin using methods much less comprehensive than those of Clairaut. 


Following Euler's suggestion, Dollond experimented on the rela- 
tive dispersion and refractive power of water and glass, and later 
of the two kinds of glass, crown and flint. 1 He found that in a 
"doublet," consisting of a convex lens of flint-glass and a concave 
lens of crown-glass, the curvatures could be so adjusted that the 
dispersions were nearly equal and opposite, while the greater re- 
fraction of the flint-glass enabled the combination to behave as a 
convex lens. An almost achromatic object-glass for telescopes was 
possible: astronomers, who had been increasingly turning to the 
reflecting telescope, were once more able to make use of the more 
reliable refractor. Attempts were made almost at once to apply 
Dollond's discovery to the manufacture of achromatic objectives 
for microscopes, a task of which the solution occupied more than 
fifty years. Perhaps most important of all, Newton's authority in 
optics was seriously checked, almost for the first time. His confi- 
dent belief, unfounded on experiment, was exposed as an error. 

The principal innovations in eighteenth-century physics were, 
however, in totally new directions, showing that the conceptual 
fertility and experimental ingenuity so marked in the preceding 
hundred years were far from exhausted. Indeed, the two major 
lines of advance were intrinsically far more difficult than those 
hitherto followed. The seventeenth century had failed, for ex- 
ample, both to place the science of heat on an exact quantitative 
foundation, and to make the conceptual distinctions which were 
essential to a true understanding of the phenomena. For these 
the vague notions of corpuscularian philosophers that heat was 
* nothing else but a very brisk and vehement agitation of the parts 
of a body' (Hooke) were a very unsatisfactory substitute. Even 
Boyle had not been able altogether to renounce the idea of "fire 
particles," or to distinguish firmly between combustion and other 
manifestations of heat. Eighteenth-century physicists found it more 
useful to think of heat as a fluid (called caloric in the new chemi- 
cal nomenclature), which flowed from hot bodies to cold; an 
hypothesis which (like that of phlogiston) proved to be radically 
mistaken but which served well at a certain stage. 

In particular, this view of heat was extraordinarily appropriate 

since most of the eighteenth-century experiments on heat were 

concerned with thermal capacity and calorimetry. Measurements 

of temperature by means of thermometers (though without regard 

1 Flint-glass contains a large proportion of lead, crown none. 


to any widely accepted scale) had become fairly commonplace 
after 1660, but for a long time no distinction was made between 
the temperature of a body, and the amount or quantity of heat 
present in it. This was natural enough, for it was believed that 
equal weights of all substances had the same thermal capacity 
that is, if equal weights of water and iron were placed in the same 
oven, they would both be raised to the same temperature in a 
given time. Fahrenheit seems to have been the first to note a con- 
trary observation. Comparing the heating and cooling effects of 
equal volumes of water and mercury, he found that the latter was 
not thirteen times as effective as the former, as the density-ratio 
would suggest, but only 60 per cent, as effective! From this Black 
judged (about 1760) that the amounts of heat required to raise 
two different bodies through the same number of degrees of tem- 
perature were in a very different proportion from that of their 
densities (assuming the volumes to be equal). Black went on to 
compare the amount of heat required to raise i Ib. of water 
through t with that required to raise i Ib. of any other substance 
through 7~, which could easily be done by mixing the two to- 
gether at different temperatures so that they attained a common 
temperature. From this experiment the relative heat-capacities 
(or specific heats) of various substances could be ascertained, 
taking that of water as a standard. 1 It was easy to imagine that 
different substances had different capabilities for absorbing the 
matter of heat (caloric), the association of the familiar notions 
fluid and capacity proving as fruitful in the science of heat as it did 
later in the science of electricity. 

Black's other discovery concerning the capacity of bodies for 
acquiring heat was even more surprising. The plausible notion 
that when a solid (such as ice, or a metal) was brought to its 
melting point as shown by a thermometer, only a small amount of 
further heat was required to liquefy it had not been challenged. 
Similarly it was thought that a minute loss of heat was enough to 
cause water at 32 F. to congeal : no discontinuity between the 
solid and liquid states, in relation to heat lost or absorbed, was 
imagined. Black, however, observed that after a spell of cold 

1 e.g. mixing i Ib. of water at f, and i Ib. of mercury at T (T > /), the 
resulting common temperature being x, the quantity of heat sufficient to 
raise the mercury through (T x) has raised the water through (x f): 
whence the ratio of the thermal capacities of water and mercury is as ( T #) 
to (x - /). 


weather masses of ice and snow would last for weeks without 
melting; were it not so 'torrents and inundations would be incom- 
parably more irresistible and dreadful. They would tear up and 
sweep away everything, and that so suddenly that mankind should 
have great difficulty to escape their ravages.' A piece of melting 
ice, he reasoned, must still be capable of absorbing a great quantity 
of heat, although the water running from it was at freezing-point. 
In other words, the ice was capable of taking up heat, without a 
corresponding increase in temperature being apparent; the only 
effect of this extra heat was the liquefying of the ice. It was latent, 
because it seemed to be c absorbed or concealed within the water, 
so as not to be discoverable by the application of the thermometer.' 
Black then proceeded to measure experimentally the amount of 
latent heat taken up by ice on its conversion into water, and by 
water on its conversion into steam. Thus he attained the concep- 
tion of a definite quantity of the " matter of heat" insensible to 
the thermometer being involved in any change of physical state; 
this "quantum" of heat was not a mere agent dissolving ice into 
water, but was a physical constituent of water differentiating it 
from ice, or alternatively, from steam. 

Later, Laplace and Lavoisier were able to perfect Black's ex- 
periments with the ice-calorimeter which they invented. 1 They 
pointed out that such quantitative determinations could be 
carried out without theoretical preconceptions, but, like Black, 
they favoured the material theory, as is very evident in Lavoisier's 
Traite Mementaire de Chimie. Like Black, they concluded that any 
sample of matter (in a given physical state, at a given temperature) 
consists of substance and heat, the absolute degree of heat being 
incapable of registration on a thermometer, and residing in all 
bodies even at the lowest attainable temperatures. Their experi- 
ments went much further than Black's in studying the evolution 
or loss of heat in chemical operations, whence it appeared that 
the theory of chemistry would need to account not merely for 
matter-reactions (syntheses, analyses, exchanges and so forth) but 
for the heat-reactions with which these are integrally associated. 
In modern terms, they had realized that questions of energy are 
involved in chemical processes; as the concept energy was unknown 
to them, however, they naturally tended to make the heat-reaction 

1 In this instrument, the quantity of heat lost by a body in falling to o C. 
was measured by the weight of water melted from a surrounding jacket of ice. 


cognate to the matter-reaction, by treating heat itself as a material 
entity, and measurements of "quantities of heat" as measurement 
of something, which would be conceived (at least in imagination) as 
existing apart from the matter whose quantity of heat was 
measured. The very obvious formulation 

ice + heat -> water; water + heat -> steam 

emphasized the dichotomy between the matter (water-corpuscles) 
identical in ice, water and steam, and the absorbed quantity of 
something measurable making the distinction between its three 
states. Attempts, throughout the eighteenth century, to measure 
the mass of heat by weighing heated and cooled bodies, which had 
a negative result, did not disturb those who held that heat was a 
weightless fluid. 1 Only in 1798 was attention called to the fact 
that bodies can evolve an indefinite amount of heat through fric- 
tion by Benjamin Thompson's (Count Rumford) experiments. On 
the material theory the quantity of heat contained in a body at 
a given temperature was limited absolutely, but in spite of this 
difficulty, the kinetic view of heat (as it was less applicable, at this 
stage, to any other phenomena than those of friction) failed to 
displace the material theory for another half-century. 

This fact is itself enough to provoke reflection among those who 
hold that quantitative experiments are infallible instruments of 
scientific progress. When the theory of heat was entirely qualita- 
tive, not to say speculative, in the seventeenth century, a more 
"correct" kinetic view prevailed. The material theory which so 
successfully resisted, in the decade 1840-50, the attrition of Mayer 
and Joule was decisively established by the quantitative experi- 
ments of Black, Laplace, Lavoisier and others. The "correct" 
kinetic view was in fact decisively obstructed by its failure to yield 
neat and easily comprehensible quantitative results, and for this 
reason it could not, perhaps, ever have been established save (as 
it eventually was) under the cloak of a generalized concept of 

In many of its aspects eighteenth-century physics represents 
the pre-history of this concept. Mechanical energy, as vis viva, and 
the power to do work, was very attentively considered. The first 

1 It is very strange that the illogicality of the concept of matter without 
weight (which has been held by some to have inspired Lavoisier's attack on 
phlogiston) was one which he himself embraced in his own theory of caloric. 


steps towards the study of chemical energy were taken by Laplace 
and Lavoisier. The very complex role of heat in physical and 
chemical changes was at least partially disclosed, and in a purely 
practical way the connection between heat energy and mechanical 
energy was of great interest to engineers, ever extending the utility 
and efficiency of the steam-engine as a prime mover. The major 
invention of this period Watt's introduction of the separate con- 
denser is said to have been inspired by Black's discovery of latent 
heat, and certainly Watt carried on his own investigations into the 
physics of heat. 1 It was clearly his purpose to squeeze the maxi- 
mum mechanical value from the "quantity of heat" contained in 
steam and so cut down the coal bills of those who bought his 
engine but the theoretical implications, in terms of a "perfectly 
efficient" engine, were only worked out by Sadi Carnot about 
1824. Heat energy in the form of invisible radiation was also 
known, and the likeness in properties between this form of heat 
and light was recognized. Experiments to find out whether light 
itself has energy for if a beam of light consisted of a stream of 
corpuscles travelling at a very high speed, their impact upon an 
opaque surface should be detectable, even though very minute 
yielded some positive effects, but these were most probably due to 
other causes. Perhaps most important of all was the elucidation 
of a new form of energy, electricity. Certainly this was the most 
striking, the most original, and the most progressive branch of 
eighteenth-century physics. The spectacle of the erect hair, the 
nasal sparks, of an electrified youth hung in silk cords from the 
ceiling excited the rather coarse humour of the age; the mystery 
of lightning drawn off down an iron rod and confined, like a jinn, 
in a Leyden bottle, was witness to the strange power of nature and 
man's intellectual mastery of it; while, at a more serious and 
prosaic level, a new corpus of experimental and theoretical know- 
ledge was taking shape, of incalculable importance for the future. 
No one could have foreseen, in Franklin's day, the extent to which 

1 It was not at all necessary, however, for Watt's purpose that the main 
cause of the wastefulness of contemporary steam-engines (the chilling of the 
cylinder and piston by the injection of cold water to produce a vacuum) should 
have been so scientifically diagnosed. An intuitive realization of the folly of 
alternately heating and cooling the same masses of metal without any produc- 
tive purpose would have been amply sufficient. So that, whatever advice Watt 
may have received from Black, it can hardly be said that the separate condenser 
was an immediate fruit of the physics of heat. 


physics was to become the science of electricity, yet already by 
1800 almost every experimental physicist was to some degree an 

All this grew from very humble origins. Gilbert had shown that 
the attractive property of rubbed amber was quite widespread in 
nature, and had coined such terms as "electric" (from Greek 
elektron = amber), and "charged body." Soon afterwards the 
mutual repulsion of similarly charged fragments of light materials 
was noticed for the first time. But the first hints of more remark- 
able effects followed upon the introduction of the first electrical 
machines, and thus anticipated the course of the later history of 
electricity: every important step was brought about by some new 
instrument or device. For electrical phenomena are not made 
manifest in nature; the few that occur (such as lightning) could 
never conceivably have been interpreted correctly in the light of 
reason. They were entirely hidden from artisans and other prac- 
tical men skilled in nature's ways, no tools or instruments of 
science or art could be easily adopted to an inquiry into electricity, 
and the human body is very limited in its reactions to electrical 
stimuli from outside. There could, therefore, be no progress in 
electrical science without means of creating charges, currents etc., 
and means of revealing their various properties. Theoretical 
rationalization was bound to be, in the very early stages, of rela- 
tively little importance, and in any case subject to extremely rapid 

The first electrical machine was a globe of sulphur or glass, 
mounted on an axle and rotated by a handle, which was rubbed 
against the hand until highly electrified. The glow, visible in the 
dark, produced by discharge between the globe and the hand was 
first noted by Otto von Guericke, who also succeeded in trans- 
mitting the electrical effect along a linen thread. Another curious 
phenomenon observed at about the same time was for long unre- 
lated to electricity. This was the luminosity in the vacuum of a 
barometer when the mercury was shaken. Only in 1745 was it 
shown that under these conditions the glass tube became electrified, 
though Hawksbee, about 1710, had caused a similar glow to 
appear upon an electrical machine worked in vacuo, and inside an 
exhausted vessel rubbed externally. Hawksbee allowed a chain 
to hang against the globe of his electrical machine, so that the 
charge would be taken to a large "prime conductor," but the next 


improvement the use of a soft rubber instead of the operator's 
hand was only introduced a little before the middle of the 

The study of conduction was taken further by Stephen Gray 
(1732), who found that charges could be transmitted along, or 
induced into, very long lines of thread when these were suitably 
supported. He was thus led to make the fundamental distinction 
between insulators and conductors, for silk filaments did not permit 
his charges to leak away, while equally fine copper wires did. 
Hair, resin and glass proved like silk non-conducting. A French- 
man, Charles Dufay, had the ingenuity to mount a variety of 
substances upon insulating supports in order to demonstrate that 
all including the metals could be electrified by friction when 
isolated from the earth; he saw that Gray's distinction between 
insulators and conductors was really more primary than the 
established one between electrics and non-electrics, to which it 
had seemed analogous. Dufay, moreover, discovered that a frag- 
ment of gold leaf, charged with an electrified glass rod, was not 
repelled (as he expected) by a piece of electrified amber, but 
strongly attracted to it. The lesson, from magnetism, was obvious 
enough; the two charges, the one "vitreous" and the other 
"resinous," were of opposite sign. In the neutral state all bodies 
contained equal quantities of both electricities; the action of fric- 
tion was to remove a part of one or the other, leaving behind 
a superfluity of the second. 

Any substance could be charged on a suitable stand. A number 
of experimenters tried to electrify water in insulating glass vessels: 
they discovered, to their distress, that if with one hand grasping 
the jar full of liquid, with the other hand they tried to take away 
the wire leading into it from the electrical machine, they ex- 
perienced a frightful shock. They had, in fact, formed a condenser 
and discharged it through their bodies: it was an easy step to 
make the "Leyden jar" more convenient by lining it within and 
without with metal foil and to learn to handle it with greater 
caution. With the aid of powerful frictional machines, and the 
large charge built up in a Leyden jar, it was possible by 1750 to 
produce very striking sparks, and discharges heavy enough to kill 
small animals or to be transmitted through long circuits of wire 
or water. Attempts were even made to estimate the velocity of 
the motion of a charge by the interval between two sparks across 


gaps separated by a long circuit: but of course without success. 
The heating effect of electricity (e.g. in melting fine conductors) was 
easily perceived as were some of the effects associated with dis- 
charge through a vacuum. Upon electrical theory the effect of the 
discovery of the condenser was profound. The dualistic hypothesis 
of Dufay was clearly susceptible of simplification: it was unneces- 
sary to suppose that there were two kinds of electricity (com- 
parable to the two poles of a magnet) for " oppositeness " could be 
taken, as in mathematics, as a difference in quantity rather than 
a difference in quality. On such a view, with a normal charge a 
body would be neutral, with an excess of electricity positively 
charged, and with a defect of electricity negatively charged. This 
view could be applied with particular success to the novel 
phenomena revealed by the condenser. 

The man who so applied and developed the unitary theory of 
electricity was Benjamin Franklin (1706-90), retired printer of 
Philadelphia, popular philosopher, later hero of the American 
revolution and elder statesman of the young republic. With his 
plain common sense and distrust of subtlety, Franklin combined 
an active scientific imagination sharpened, perhaps, by his almost 
complete ignorance (during the creative stages of his work) of 
European theories. In his opinion, which strongly reflected the 
corpuscularian ideas of the age, electricity was a fluid, consisting 
of particles mutually repelling each other, but strongly attractive 
to other matter, which distributed itself uniformly as an "atmo- 
sphere" about a body or connected system of bodies. Electrification 
was a process whereby an excess of this fluid was collected upon a 
particular body, such as a glass rod, by friction or other means, so 
that it became positively charged; or removed from it so that it 
became negatively charged. Franklin believed (mistakenly) that a 
discharge was simply a transfer, often in the form of a unidirec- 
tional spark, from a body more highly charged with the fluid to 
one less charged; and the repulsion between two positively charged 
cork balls was readily attributed by him to the repulsion between 
the excess of electric particles. When Franklin became aware that 
negatively charged bodies also repel each other, he encountered a 
difficulty which his theory could not overcome. He fully realized 
the importance of the deduction, from his fluid theory, that within 
a closed system the quantity of electricity must be conserved: a 
person, placed on an insulating stand, could collect a positive 


charge upon a glass rod by rubbing it, but only by electrifying his 
own body negatively to an equal degree, that is, by forcing 
electricity from his body into the tube. By inverse reasoning from 
the same principle Franklin explained the action of the condenser, 
for every addition of electricity to one of its surfaces produced a 
corresponding loss (to earth) from the other, as shown by the fact 
that the Leyden jar could not be charged unless one plate was 
earthed. The total quantity of electricity in the jar was always 
constant, only its distribution being modified by electrification 
since a connection between the plates (under any conditions) 
ensured a return to the neutral state. Franklin regarded the 
condenser as fully charged when all the electric " atmosphere" 
had been driven off the earthed plate, for then no more could be 
added to the positive plate, since this would have increased the 
total quantity present. 

This theory, and the experiments intended to confirm it, of 
which many were already familiar to European electricians, were 
warmly welcomed, as indeed were all contributions to science 
from the New World at this time. But at first Franklin's letters did 
not carry conviction, nor did they have any very dramatic effect. 
Strangely, it was a less creditable, but more showy, suggestion 
that brought about his lionization. Many electricians had noted 
the similarity between the electric spark and lightning and be- 
tween the accompanying crackle and thunder, speculating on the 
possible identity of the two effects; there was therefore nothing 
very new in Franklin's similar speculation. He, however, had 
noticed particularly the powerful action of pointed conductors in 
"drawing off" a charge silently and conjectured that if thunder- 
clouds were, as he supposed, positively charged, the fact could be 
revealed by drawing electricity away to a high, pointed conductor. 
Having described the experiment, he failed to execute himself 
(for a variety of reasons, among which lack of courage was 
certainly not one). It was first successfully performed in France, 
soon after the translation of Franklin's early letters was made. 
The well-known "Kite experiment" at Philadelphia was carried 
out, with a like result, before news of the French attempts and 
of his own sudden fame as the tamer of lightning had reached 
Franklin in America. Richmann, at St. Petersburg, was the first 
"martyr" to the pursuit of this new branch of electrical 


Until the moment of Franklin's intervention (1746-55) elec- 
tricians had been wholly preoccupied with qualitative effects. 
Most of the material published had dealt with the description of 
phenomena, which the experimenters had sought to explain in the 
light of ad hoc hypotheses, each of them jejune in varying degrees 
and inadequate to explain all the facts. Franklin himself had not 
sensibly modified this state of affairs, for though his single-fluid 
theory was more comprehensive than any other, it was not com- 
pletely so, nor did it really rise above the phenomenalistic level of 
his work. The revisions he introduced himself were sufficiently 
serious for it to be classified (logically) as no more than a pro- 
visional working hypothesis. The investigation of new effects 
continued to be of some importance as, for example, in the study 
of induction, of the role of the dielectric in condensers, and of 
pyro-electric phenomena but a more rigorous inquiry into the 
quantitative aspects of electrical phenomena grew up alongside it 
during the second half of the century. In accordance with the 
general principle already mentioned (p. 237), the electrician's 
apparatus, which had formerly been limited to the revelation of 
the qualities of electricity, now began to be adopted to measure 
quantities. An interesting instance of this is the elaboration, from 
the pith-balls and gold-foils formerly employed to test for the 
existence of charges, of the torsion-balance of Coulomb (c. 1 784) 
and the electrometer of Bennet (1787). Hitherto, though the 
achievement of solid additions to knowledge and the ingenuity of 
theorization must be duly recognized, experiment and thinking 
in electricity had been amateurish, for the former had often 
partaken of the nature of a parlour game, and the latter had 
included much extravagance. The rapid success of Franklin, 
starting almost from zero, is an indication as well of the super- 
ficiality of the subject, as of his own ability. Now, however, 
electrical science began to acquire a more serious status as a 
branch of physics. 

Among the first to deny themselves the pleasure of declaring 
what electricity is, was Joseph Priestley. His precisely regulated 
experiments on conduction contain the seeds of later ideas of 
electrical resistance; like ^Epinus a little earlier, he found that 
the distinction between conductors and insulators was far from 
absolute. Priestley used the length of a spark-gap, across which a 
discharge would jump instead of traversing a long circuit, as a 


measure of the circuit's resistance. He repeated Franklin's experi- 
ment to show that there is no charge inside an electrified hollow 
vessel of metal, and deduced from it (by analogy with a familiar 
theorem on gravitational attraction) the opinion that c the attrac- 
tion of electricity is subject to the same laws with that of gravita- 
tion ' that is to say, it varied proportionately to the inverse square 
of the distance. This was perhaps the first proposition about 
electricity that could be formulated mathematically, and more- 
over a prediction to which experimental verification could be 
applied. This was done by Robison two years later (in 1769), by 
Cavendish, and by the French engineer Coulomb. Cavendish 
designed an ingenious apparatus by which one metal sphere could 
be enclosed within another, with or without electrical contact 
between the two, finding that the charge applied was invariably 
confined to the outer sphere. He ascertained that the electric 
force must vary as the square of the distance within limits of 
db ! per cent. Many other quantitative experiments (partially 
anticipating the later work of Michael Faraday) were performed 
by him about 1771-3, which with typical unconcern he kept 
entirely to himself. He was the first electrician to adopt a standard 
of capacity (a metal-covered sphere, 12 i inches in diameter), with 
which he compared the capacities of other bodies, stating these 
as "inches of electricity," that is as the diameters of spheres of 
equal capacity, and to realize that the charge upon a conductor 
is proportional to both its capacity and the " degree of electrifica- 
tion" applied. By "degree of electrification " Cavendish under- 
stood the extent to which the "electric fluid" was compressed 
into a body, so that he approached very near to the later concept 
of electrical potential. He also knew that the capacity of a con- 
denser varies with the material of the dielectric, and made several 
measurements of what Faraday was afterwards to name specific 
inductive capacity. He measured the conductivity of a variety of 
solutions in glass tubes, discovering that this was independent of 
the size of the discharge passed through them. Considering that 
he made use of crude pith-ball electrometers, and relied upon his 
own senses to compare the violence of electric shocks, the numeri- 
cal results he obtained were astonishingly good. All this work, 
unfortunately, had no effect upon the subsequent progress of 
electrostatics, as it was totally unknown. The inverse square law of 
electric force was first demonstrated in print by Coulomb (1785), 



in experiments one of which was similar to that of Cavendish, 
while others made use of Coulomb's torsion-balance for the direct 
measurement of forces. These experiments in turn served as the 
foundation for Poisson's mathematical study of electrostatic forces 
in the early nineteenth century. 

The interval was marked by no important discoveries. This was 
undoubtedly due in very large part to the sudden fascination of a 
new set of phenomenalistic effects, wholly unsuspected, in which 
electricity appeared in another of its Protean forms. Hitherto the 
manifestations of electricity had been limited to two groups: (a) 
shocks and sparks, (b) repulsions and attractions. To the first 
group belonged, besides the laboratory effects, those of lightning 
and the torpedo or electric fish. No serious physiological study had 
been made of the first group of effects it was merely known that 
a shock produced violent muscular contractions, and followed a 
more or less direct path through the body though the adminis- 
tration of shocks was (like most other things) regarded as having 
a medical value. Hence experimentation in electricity had been 
practically confined to the exploitation of the attraction-repulsion 
effect in a variety of different ways. This in turn had its influence 
on theory. In the first place electricity was literally regarded as an 
effluvium, a particulate atmosphere surrounding the charged body. 
How, Newton had asked, can an electrified body 'emit an ex- 
halation so rare and subtle, and yet so potent, as by its emission 
to cause no sensible diminution of the weight of the electrick 
body . . .P' 1 Then again, the Abbe Nollet (1700-70) had sup- 
posed repulsion and attraction to be the work of outflowing and 
inflowing streams of the electric fluid. Later in the century, the 
analogy between electrical and gravitational attraction becoming 
more obvious, the electric effluvium seemed as absurd as the gravi- 
tational effluvium of pre-Newtonian physicists, and "action at a 
distance" was accepted. Thus the theory of electricity passed 
through various phases of mechanical explanation, much as the 
theory of gravity had done in the seventeenth century, owing to 
the focussing of attention upon its mechanical manifestations. 
Just as the weightless fluid caloric was capable of mechanically 
expanding bodies, so the weightless electric fluid was capable of 
putting them in motion even of causing continuous rotation in 
a light wheel. Mechanical analogies really justified the concept of 

1 Opticks, Query 22. 


electricity as a fluid, whose particles were capable of action at a 
distance, for electricity could flow along conductors, filling bodies 
to their "capacity," and yet be impeded by "impermeable" sub- 
stances. Borrowings from the languages and ideas of hydraulics 
are indeed obvious; Cavendish's concept of electrical "pressure" 
showed how fertile they could be. 

It is the nature of a fluid, even an elastic fluid, to flow, and the 
study of "electrostatics" had actually embraced some investiga- 
tion into the flow of electricity along conductors. But the effects 
produced by the flow of charge (under the prevailing conditions of 
experiment) were not striking as compared with the mechanically 
obvious effects of a static charge. The motion of electricity, re- 
vealed by a spark or a shock, was in any case a transient event, 
restoring the apparatus to a condition of electrical neutrality, so 
that the phenomenon of electricity had always appeared to be 
discontinuous, indeed so much so as to be almost adventitious. 
Charges were immediately annihilated by conduction to earth, 
and no perfectly insulating material was known. They were 
formed only by the chance electrification of a cloud, or by the 
discontinuous action of friction, which suggested that they were 
mechanically produced. The appearance of all the known effects 
depended upon the discontinuity in the movement of electricity, 
leading to the accumulation of large static charges. 

The discovery of new manifestations of electricity was thus of 
absorbing interest for a variety of reasons. These were not the 
result of mechanical action, nor were they themselves mechanical 
in nature. They were continuous, and they required no effort. In 
the prevailing theory some segregating action was necessary to 
bring about the conditions of electrification the fluid had to be 
impelled from one body to another, leaving the former unnaturally 
empty and making the latter unnaturally full so creating an un- 
balanced state which nature herself sought to adjust at the first 
opportunity. The new effects predicated no such positive action; 
it was not necessary, in order to produce them, to build up 
mechanically an artificial "degree of electrification." 

The differences between the new phenomena and the old were 
sufficient, at first, to obscure the connection between them. About 
1780, in the laboratory of the Italian anatomist Luigi Galvani 
(1737-98) at Bologna, an assistant happened to notice that when 
he touched with his scalpel the crural nerve of a frog's leg which 


he was dissecting the muscles were violently contracted. It was 
remarked that this occurred while a spark was being drawn from 
an electrical machine placed on the same table. Galvani repeated 
the strange experiment, under the same conditions and with a like 
result. He introduced many variants, all of which proved that the 
experiment failed unless the operator was in electrical connection 
with the nerve, and the frog's leg effectively earthed. From this 
Galvani suspected that some sort of electrical circuit was involved 
for muscular contractions were known to occur when discharges 
were sent through dead animals even though the frog was not 
directly linked to the electrical machine. Many experiments were 
performed at this stage to gain conviction that the stimulus was 
really electrical. The next major step was a successful demonstra- 
tion that lightning flashes acted upon the limb in an identical 
fashion when similar electrical connections were made to it. In the 
course of these atmospheric experiments Galvani observed that 
frogs hung from an iron lattice in his garden by brass hooks pene- 
trating into the spinal marrow gave occasional convulsions. Once, 
happening to press one of the hooks firmly against the iron, he saw 
immediate contractions. At first he thought that these were due to 
the escape to earth of some atmospheric electricity accumulated 
in the frog. To test this suspicion he re-created the same condi- 
tions indoors, placing the frog on an iron plate and pressing the 
brass hook firmly against it. Still the convulsions occurred ( 1 786) . 
Other combinations of metals, or even a circuit through his own 
body, or a homogeneous wire, with which he made a " conducting 
arc" between nerve and muscle, had the same effect, but not in- 
sulators. Again Galvani satisfied himself by elaborate experiments 
that the decisive circumstance was the existence of a path along 
which electricity could flow. 

Had he been a more enthusiastic electrician, Galvani might 
have inquired more fully into the curious situation in which a 
spark from an electrical machine or Leyden jar could influence 
a frog's leg insulated from it. Instead, after his discovery that the 
spark was unnecessary provided that a direct connection was made 
between nerve and muscle, he abandoned that subject. At this 
point two other lines of inquiry suggested themselves. He could 
examine more carefully the nature of the electrical circuit, and 
this he did in some detail, finding that some metals were less 
effective than others in the conducting arc, that liquids could be 


used, and that a single conductor was less effective than one made 
up from two metals. But he did not attach great importance to the 
bimetallic circuit, because convulsions were obtained with a single 
conductor. He was therefore led to concentrate upon the second 
line of inquiry, convinced as he was that Leyden jars, machines, 
thunderstorms and other familiar sources of electricity could be 
excluded from his explanation of the phenomena, and that the 
conducting arc was simply an ordinary conductor of electricity. 
The physiology of the frog's reactions now drew his attention, 
since it appeared that the mere electrical connection of nerve and 
muscle was capable of causing the same contractions as the appli- 
cation of an electrical stimulus to these parts. In the former case 
the electricity moving along the conductor must have been sup- 
plied by the frog itself. To hypothesize further still, was not the 
stimulus given by a nerve to a muscle always electrical, for (as he 
said) ' the hidden nature of animal spirits, searched for in vain 
until now, appears at last as scarcely obscure' it was electricity! 
Prepared in the brain, and distributed by the nerves, this "animal 
electricity" on entering the muscles caused their particles to at- 
tract each other more strongly, and the fibres correspondingly to 
contract. In the muscles also electricity was stored, as in a Leyden 
jar, so that from a communication between them and a nerve 
ensued the convulsions witnessed in his last series of experiments. 
Thus Galvani brought his electrical discoveries to a close by 
riding off on a physiological hobby-horse, abandoning physics in 
order to debate how his new knowledge of animal electricity 
might be applied to the cure of disease. Many other scientists 
eagerly followed his example. 

An alternative and less dramatic interpretation would have 
made the frog's leg merely a sensitive detector of an electric 
current through the circuit linking nerve and muscle, as in Gal- 
vani's first experiments, the stimulus for the convulsions being 
always supplied by an external source of electricity. On this view, 
little compatible at first sight with his later discoveries, Galvani 
had not discovered a new example of animal electricity (already 
familiar in electric fish) ; he had invented a new electrical instru- 
ment, and a new source of electricity in motion the bimetallic 
conductor of his last experiments. This was the interpretation of 
Galvani's work put forward by Alessandro Volta (1745-1827) of 
Pavia in 1792, about a year after the first account of them was 


published. At first Volta had given credence to Galvani's own 
explanation, hailing his discoveries as no less epoch-making than 
those of Franklin. Gradually, however, Volta uncovered facts 
which compelled him to differ from Galvani. The most delicate 
electrometer revealed no electricity in animal tissues; to cause the 
muscles to contract, it was only necessary to apply an electrical 
stimulus to the nerves, and not to the muscles themselves; and to 
create this stimulus a bimetallic junction was essential. 1 Finally, 
in a letter destined for the Royal Society, Volta asserted that the 
frog's leg as prepared by Galvani was nothing other than a deli- 
cate electrometer, and that most of the phenomena attributed to 
animal electricity were ' really the effects of a very feeble artificial 
electricity, which is generated in a way that is beyond doubt by the 
simple application of two different metals. 5 

By this time [wrote Volta in November 1 792] I am persuaded that 
the electric fluid is never excited and moved by the proper action 
of the organs, or by any vital force, or extended to be brought from 
one part of the animal to another, but that it is determined and con- 
strained by virtue of an impulse which it receives in the place where 
the metals join. 2 

He had invented a new theory of contact electricity, and was 
compelled, in its defence, to criticize the physiological views of 
the wretched Galvani, who died in despair after some years of 
futile controversy. Meanwhile Volta continued his experiments. 
He found that the metals whose contact caused a flow of electric 
fluid could be arranged in a definite order, that other conductors 
such as carbon had the same effect, and that any moist conductor, 
such as water, served to bridge the different metals as well as 
animal tissues. By 1795 he had propounded the "law" that when- 
ever two dissimilar metallic conductors were in contact with each 
other and a moist conductor, a flow of electricity took place. In 
1 796 he demonstrated that the mere contact of different metals 
produced equal and opposite charges upon them, made visible 
by the electroscope. This was the first proof of the identity of 
galvanic and frictional electricity, of which Volta had always been 
convinced. The charges, which appeared to be indefinitely pro- 
curable, were positive or negative according to the order of the 

1 Volta ascribed the effects obtained by Galvani with a single conducting 
element to lack of homogeneity and other differences in the metal. 

2 Opere (Firenze, 1816), vol. II, pt. i, pp. 165-6. 


metals used in the series which he had discovered earlier. 1 The 
intensity of the effects produced was still minute, and Volta real- 
ized that it could not be increased by multiplying the number of 
bimetallic junctions so much was obvious from the distribution 
of charges. The case was different when two or more pairs of metal 
plates in contact were joined together, not directly or by use of a 
third metal conductor, but by one of the moist conductors such 
as salt water, either placed in cups into which the metal plates 
were dipped, or soaked into cardboard discs inserted between each 
bimetallic pair. In this arrangement (described by Volta in 1800) 
the intensity of the effects produced was proportional to the number 
of the pairs of plates, so that Volta could charge condensers, 
produce sparks, and give severe shocks. This " artificial electrical 
organ" (which Volta compared to the natural electrical organs of 
certain fish), electromotor, or pile, as it was afterwards called, was 
as he said like a feebly charged Leyden jar of immense capacity, 
for it would yield electricity continuously. The continuity of the 
flow of electricity from terminal to terminal of the pile was par- 
ticularly emphasized by Volta in his descriptive letter to the Royal 
Society; as there was no instrument suitable for the detection of 
continuous currents, he had to quote his physiological sensations 
in proof of their existence. The situation was paradoxical, but none 
the less real. 

It seems clear that Volta, who was little interested in the 
chemical effects associated with the passage of an electric current, 
completely misunderstood the functioning of the single cells in 
his pile. He regarded the "electric force" as originating from the 
contact of two different metals, not from the reaction of these 
with the moist electrolyte between them. In modern theory the 
voltaic cell consists (for example) of copper, electrolyte and zinc; 
but to Volta himself the copper-zinc junction was the "cell," 
the source of electricity, and the electrolyte served merely to 
connect these together without neutralizing the charges collected 
on the metals. He was still thinking, essentially, in electrostatic 

The action exciting and moving the electric fluid is not due, as is 
falsely believed, to the contact of the humid substance with the metal; 
or at any rate it is only due to that in a very small degree, which may 

i.e. -f Zn, Pb, Sn, Fe, Cu, Ag, Au, C . These experiments were only made 
possible by Volta 's improvement of the electroscope in earlier years. 


be neglected in comparison with that due to the contact of two 
different metals, as all my experiments prove. In consequence the 
active element in my electromotive apparatus, in piles, or in cups, or 
in any other form that may be constructed in accordance with the 
same principles, is the mere metallic junction of two different metals, 
certainly not a humid substance applied to a metal, or included be- 
tween two different metals, as the majority of physicists have claimed. 
The humid layers in this apparatus serve only to connect the metallic 
junctions disposed in such a way as to impel the electric fluid in one 
direction, and to make this connection so that there shall be no 
action in a contrary direction. 1 

This theory did not long survive. As Nicholson pointed out in 
1802, an electric current could be drawn from cells consisting 
of one metal and two electrolytes, and by this time already the 
work on the new form of electricity was assuming a markedly 
chemical character. Fabroni, in 1 796, had observed the oxidation 
of one of a pair of plates of different metals joined together and 
immersed in water. Ritter had perceived that the order of the 
metals in Volta's series was a chemical order that of their 
exchange in solutions of their salts. Very soon after Volta's letter 
of 1800 reached London, Nicholson and Carlisle, experimenting 
with the first of his piles to be constructed in England, had, by 
following up a chance observation, electrolysed water into oxygen 
and hydrogen. Solutions of metallic salts were rapidly decomposed 
by the same means. Even in the mid-eighteenth century chemical 
changes had been effected by electrostatic discharges, so that a 
way of proving yet more firmly the identity of frictional and gal- 
vanic electricity offered itself. It was certain that electrical forces 
could bring about a chemical change; was the converse also true? 
Humphry Davy asserted this boldly. In 1800 he pointed out that 
the voltaic pile could act only when the electrolyte was capable 
of oxidizing one of the metal elements, and that the intensity of 
its effect was directly related to the readiness of the electrolyte to 
react with the metal. Six years later, in a Bakerian lecture, Davy 

In the present state of our knowledge, it would be useless to attempt 
to speculate on the remote cause of the electrical energy, or the 
reason why different bodies, after being brought into contact, should 
be found differently electrified; its relation to chemical affinity is, 

1 Opere, vol. II, pt. ii, p. 158; (written in 1801). 


however, sufficiently evident. May it not be identical with it, and an 
essential property of matter? 

For on Davy's view, in accord with his experiments on contact 
electricity, in the simplest types of electrochemical activity an 

alkali which receives electricity from the metal would necessarily, on 
being separated from it, appear positive; whilst [an] acid under similar 
circumstances would be negative; and these bodies having respect- 
ively with regard to the metals, that which may be called a positive 
and a negative electrical energy, in their repellent and attractive 
functions seem to be governed by laws the same as the common laws 
of electrical attraction and repulsion. 1 

Thus Davy held that the concept of affinity, upon the basis of 
which the phenomena of chemical combination were explicable, 
was itself to be explained in terms of electrical forces or "energies." 
His prediction that electrolysis would prove to be a most valuable 
tool of chemical analysis was well borne out in the following year 
when, by this method, he isolated potassium from potash and 
sodium from common salt. 

In the same lecture of 1 806 Davy presented his electrochemical 
theory of the voltaic pile. He thought that, owing to the opposite 
"electrical energies" of the metals used, decomposition of the 
electrolyte occurred by the breaking down of its natural affinity, 
as in a solution of salt (for example) c the oxygene and the acid 
are attracted by the zinc [plate], and the hydrogene and the 
alkali by the copper [plate].' The production of electricity, when 
the plates were joined in a circuit, was continuous because the 
chemical action, that is the solution of zinc in the electrolyte and 
the evolution of hydrogen from the copper plate, was continuous: 
'the process of electro motion continues, as long as the chemical 
changes are capable of being carried on.' Davy also believed that 
owing to the tension created by the electrically opposed metals, 
the whole of the electrolyte was in a state of continual decompo- 
sition and recomposition. There were obvious defects in this 
account, but it had the great merit of integrating in one hypo- 
thesis the facts of contact electricity, discovered by Volta, and the 
facts of chemical change associated with the flow of electric 
current through compound bodies. Evidently Davy realized that 
the action of electrolysis and of the voltaic pile are essentially the 

1 Philosophical Transactions, 1807, pp. 33, 39. 


same, though the one requires an electric current to be applied, 
and the other yields a current. At the same time he recognized 
that electricity could be produced without chemical change, and 
chemical changes occur with which no electrical effects were 
associated; therefore chemical changes could not be 'the primary 
causes of the phenomena of GALVANISM.' 

The scope of electrochemical theory was extended and defined 
by the Swedish chemist J. J. Berzelius, whose first memoir ap- 
peared in 1803. To pursue it farther would be to exceed the limits 
of this volume. What may be noticed is the significance of the 
sudden emergence of this young branch of science, electricity, as 
a bridge between physics and chemistry. A situation in which 
certain phenomena had been studied for their physiological 
significance, then reinterpreted by a physicist, and finally taken 
up by chemists, was absolutely unprecedented in science. The 
still-mysterious unity of nature was once more vindicated. For 
twenty years the chemical manifestations of electricity dominated 
research almost as completely as its mechanical manifestations 
had in the eighteenth century; it was not until about 1820, with 
the work of Oersted and Faraday, that the mechanical effects of 
current electricity (provided by the voltaic battery) attracted 
attention. Similarly, and inevitably, the mathematical theory of 
electric current was many years younger than that of electric 
charges, since in each case the mathematical theory was developed 
from the quantitative measurement of mechanical effects. All 
this was the fruit of the one crucial invention of the voltaic pile, 
the battery as it was soon to be called, to which Volta was led 
systematically from the first chance observations of Galvani. The 
chemical effects of transient electrostatic discharges had aroused 
little interest, whereas those of current electricity were spectacular. 
They raised the question of the relationship between the thing 
"electricity" or "electric fluid" and ordinary ponderable matter 
in a new and challenging form. Not only did electricity appear 
(in Davy's words) as c an essential property of matter' this, after 
all, in a different context, was the conclusion already drawn by 
Franklin and Dufay it was rather that electricity was an active 
and determinant concomitant of matter without which, according 
to Davy and Berzelius, the chemical behaviour of the elementary 
forms of matter would be inconceivable. It was a logical conse- 
quence of the electrochemical theory that electricity was very far 


from being a kind of discontinuous abnormality, of concern only 
to the curious electrician who took pains to disturb bodies from 
their normal condition of comfortable neutrality. Electricity was 
not an adventitious atmosphere, or other circumstance, like 
humidity, which could be left out of account except for very 
special circumstances. From being casual, the rapid progress of 
ten years rendered it causal, having a function deeply involved 
in the differentiation of the various species of matter. Within a 
few more years the physicist was constrained to follow the chemist 
in making necessary adjustments so that he too could own in 
what sense electricity was "an essential property of matter," 
thus commencing his long ascent to the truth that the concepts 
" electricity" and " matter" are not complementary, but actually 
inseparable. In short, through the electricians' research, the link 
between the mathematical conception of matter, begun by 
Newton, and the empirical (or at least pragmatic) conception of 
matter proper to chemistry, was at last indicated although it is 
even yet far from being completely established. 


MUCH more has been learnt about Nature, from the struc- 
ture of matter to the physiology of man, in the last century 
and a half than in all preceding time. Of this there can be 
no doubt. But the scientific revolution ends when this vastly de- 
tailed exploration began, for it was that which made such investi- 
gation possible. At this point, in the early nineteenth century, a 
scientific paper on almost any topic is intelligible as a direct pre- 
cursor to research which still continues. With infinitely feebler 
tools, but with the same insistence upon accuracy in observation, 
the same confidence in quantitative experimentation, the same 
enmeshing of theory, hypothesis and factual reporting which 
philosophers then and now found so resistant to logical analysis, 
men were tackling their problems as scientists today are tackling 
far more complex ones. 

It has become almost a truism to assert that the development 
of natural science is the most pregnant feature of Western civiliza- 
tion. With technology and this is hardly any longer an independ- 
ent characteristic it is the one product of the West that has had a 
decisive, probably permanent, impact upon other contemporary 
civilizations. Compared with modern science, capitalism, the 
nation-state, art and literature, Christianity and democracy, seem 
regional idiosyncrasies, whose past is full of vicissitudes and whose 
future is full of dark uncertainty. Each of these features of Western 
civilization has made its contribution to the genesis of science, to 
which perhaps their combination was essential, but one may 
imagine that science can flourish after one or all of these has lost 
its historic individuality. Indeed, that is already happening. 
Modern science was the offspring of a form of society which has 
lasted some four hundred years, playing a dominant role in world 
history; that form of society is now in dissolution, but it seems un- 
likely that science will necessarily disappear with it. For this, more 
than any other feature of Western society, has been the cause of the 
changes that we witness, and this also will be the most powerful 
influence on the moulding of a future society. 

If this much or even a fraction of it be granted, it seems 



unfortunate that we understand the genesis of modern science as 
little as we do. The modern study of Nature alone has had a de- 
termining effect upon the course of civilization, on history in its 
political, economic and intellectual totality. The science of Egypt 
and Babylonia, China and India, Greece and Islam and medieval 
Christendom had no such effect. The recovery of it by historians 
contributes little in a positive way to the understanding of the rise 
and decay of these societies, though such work does illuminate the 
origins and peculiarities of modern science. Among the challenges 
to which these societies responded successfully, or failed to meet, 
the ubiquitous challenge of Nature was certainly one; but the 
organized, conscious, rational response to it that we call science 
was of minor importance. Because of this, because some of these 
earlier strivings with Nature are continuously connected, and 
because all of them share certain common characters distinguish- 
ing them from modern science, they may be grouped together as 
intermediate between yet more primitive attempts to explain and 
master the mysteries of man's environment, and modern science. 
We know that modern science emerged from this intermediate 
stage, from which no other society than the recent western Euro- 
pean was capable of escaping, and it is this emergence that we do 
not adequately comprehend. 

Many questions have been cursorily handled in this book be- 
cause satisfactory discussion would require a different and much 
more extensive treatment. Perhaps it is not possible yet. Little is 
known about the immediate pre-history of the scientific revolu- 
tion, which seems to demand a fundamental revision of the con- 
cept of the Renaissance: the relationship (for example) between 
Oresme and Leonardo, between Leonardo and Galileo, as men 
each thinking about Nature in a different way, is still obscure. 
Equally so are the relations of art, technology and science at this 
critical period, though it is easy to frame hypotheses, and conse- 
quently the whole problem of the connection between the changes 
in society and the concurrent changes in science is involved in 
doubt, to all but the dogmatic Marxist. Above all, the crucial 
question of the scientific revolution is seen through a veil which 
philosophers have hardly begun to raise. Why do men commit 
themselves to one kind of proposition about Nature rather than 
another? Why do they (in the absence of factual guidance) find 
one type of statement more plausible than an alternative? Why 


prefer discourses about corpuscular streams, to talk of spirits, when 
there is no evidence for either? Why believe (or not believe) in the 
existence of the vacuum? Such questions are less relevant to the 
understanding of recent science (though perhaps not wholly 
negligible), but to the understandings of its origins they are vital. 
Men's thoughts and actions were modified in ways that we simply 
cannot ascribe to the results of observation and experiment; by 
such standards, for example, the whole history of Cartesian science 
is utterly incomprehensible. 

Why do men reject one kind of science in favour of another? 
Why in modern Europe alone did they move from the intermediate 
to the modern stage? The answer cannot be simple, or single. It 
requires psychological and philosophical insight, as well as a com- 
mand of the historical facts, to which we have as yet scarcely at- 
tained, for the operation, the incidence, and the impact of the 
creative intellect are almost unknown. We cannot rely only upon 
appeal to experiment, observation, measurement, or any other 
over-simplification of the complex processes of science, to present 
us with a solution to this problem. Still less hopeful is the economic 
interpretation of the history of science, which seeks to tell us why 
men sought for control over natural forces, but cannot explain 
how they were able to acquire it. The economic motive may have 
made their attitude to Nature less disinterested, but cannot alone 
have changed its character. So, too, we recognize that precision 
in measurement has been of great importance, that experiment 
is the touchstone of hypothesis, that to the percipient observer the 
unexpected is always a fertile challenge. Yet many of the most 
dramatic challenges in the history of science have issued not from 
the unexpected, not from the spectrum that was oblong instead of 
round, not from the frog's leg that jerked instead of remaining 
still, but from the orthodox, the expected, the familiar pattern of 
experience and thought. What predisposed men to struggle for the 
moving earth, atomism, evolution, and so disturb the calm quies- 
cence of their time when no awkward barrage of fact enforced 
their turbulence? For, contrary to the straightforward inductive 
view of science, it has often happened that men have looked for 
facts to demonstrate a theory, as Galileo, Boyle and Newton did, 
without science being any the worse for that. Perhaps the finest 
minds are capable of stretching far beyond the immediate war- 
ranty of facts. 


If we admit so much, we may admit more. If modern science is 
not merely an elaborate digest of pointer-readings, then it is the 
more obvious that the scientific revolution involved more than 
the discovery of ways of making such readings and digesting them 
into a coherent synthesis. In the growth of modern science creative 
imagination, preferences, assumptions and preconceptions, ideas 
of the relations of God and Nature, arbitrary postulates, all played 
their parts. Here then is the crux; that we cannot write the full 
history of science save by reflecting the operations of original 
thought, which we do not understand; and that we cannot exclude 
from science, which is rational, the influence of factors which are 


CERTAINLY naturalistic representations, both botanical and zoological, 
may be attributed to the medieval period but only to its beginning 
and end. Such are to be found in the Greek Codex Vindobonensis (fifth 
century) or in the Latin herbal of Pseudo-Apuleius (seventh century) ; in 
both, however, there is already evidence of degeneration from the best 
Hellenistic models. They occur again in the works of miniaturists and 
other artists from the end of the fourteenth century onwards. Between 
these periods formalism and symbolism flourished and 'it is safe to 
assert that at the beginning of the thirteenth century scientific botanical 
illustration reached its nadir in the west' (Blunt). The herbal was then 
a mere uncritical catalogue, illustrated by figures which are purely 
conventional and heavily stylized. Botanical knowledge revived under 
the influence of the translators, as in the De Plantis of Albert the Great 
(c. 1200-80), the Herbal of Rufinus (c. 1290) and the Buck der Natur 
of Conrad von Megenburg (1309-74), all of which show occasional 
evidence of first-hand observation. Some originality is also shown in 
utilitarian writings of the thirteenth century and later dealing with 
hunting, falconry and agriculture. But the revival of naturalistic illus- 
tration was wholly the work of the artist, during the first stages of the 
Renaissance. Some of the best early representations of plants come 
from the brushes of Botticelli or the brothers van Eyck, as later from 
Durer and Leonardo. Manuscripts equally prove that it was the artist, 
not the man of learning, who returned to the natural model. Some ex- 
cellent figures, like those of Cybo of Hy&res, are purely decorative and 
have no relation to the text they adorn. The almost contemporary 
Burgundian school of illuminators and Italian artists developed in the 
first years of the fifteenth century great technical and artistic skill in 
the representation of plants, producing such masterpieces as the herbal 
of Benedetto Rinio, prepared by Andrea Amadio, now preserved at 
Venice. The earliest printed herbals, however, still maintained the old 
stylized convention, seen for example in the English Crete Herball (1526). 
Only with the work of Brunfels (Herbarum viva icones, 1530-36, illus- 
trated by Hans Weiditz) and of Fuchs (Historia stirpium, 1542, illustrated 
by Albrecht Meyer) was naturalistic interpretation transferred to the 
wood-cut block. 

1 Gf. Charles Singer: From Magic to Science (London, 1928); and "The herbal 
in antiquity and its transmission to later ages," J. Hellenic Studies, vol. XLVII, 
1-52; Wilfrid Blunt: The Art of Botanical Illustration (London, 1950). 

369 24 




THE geometrical equivalence of the geostatic and heliostatic methods 
of representing the apparent motions of the celestial bodies, adopted by 
Ptolemy and Copernicus respectively, is not often clearly emphasized 

though it is vital to any discussion of 
the nature of the change in astro- 
nomical thought effected by Coper- 
nicus. In a simplified form it may be 
easily demonstrated. 

Upper Planets (Fig. 11). On the 
Copernican hypothesis, O is the 
place of the sun, B that of the earth 
which has revolved through any 
angle COB, and D that of a planet 
which in the same time has revolved 
through the angle COD. The appar- 
ent position of the planet is on the 

T- TT line BD. Transposing this into Ptole- 

FIG. n. The Upper Planets. . A ^v i i i A 

rr maic terms, O is the fixed earth, A 

the sun, and D the centre of the planet's epicycle. If F is the place of 
the planet in the epicycle, then DF:DO = BO:DO. Moreover, AOB 
is a straight line, and ZFDO = /.COB /.COD = ,/ BOD. These 

relations follow from the form of the 
constants used by Ptolemy and Co- 
pernicus respectively (p. 15). Thus 
the apparent position of the planet 
is given as before, since the line FO 
is parallel to BD, and the triangles 
AFO, BDO, are identical. 

Lower Planets (Fig. 12). Here the 
situation is slightly different. The 
Copernican representation is similar 
to that given above, with the sun at 
O, earth at B, planet at D, and the 
position given by the line BD. On 
the Ptolemaic representation the 
central earth is at O, the sun at A, 
and the centre of the planet's epicycle is located on the radius AO. 
Values for the radii of the deferent and epicycle may be chosen so that 
D'FrD'O = DO:BO, provided that D'F + D'O<AO = BO. As be- 

FIG. 12. The Lower Planets. 


fore, these relations follow from the form of the constants adopted by 
Ptolemy and Copernicus. For the same reason the velocity of rotation of 
F about D' is such that Z.OD'F = /.GOD - /.COB = /.BOD. Thus 
it follows (as with the upper planets) that FO and BD are parallel, and 
that the maximum elongation of the planet from the sun is the same on 
either hypothesis. 

It may be noted that since any geometrical complexity added to one 
representation may be duplicated by a corresponding one in the other, 
the apparent positions of the planets are always the same on either 
hypothesis. In the case of the inferior planets, Venus and Mercury, 
however, the triangles OD'F, BOD, are similar but not identical. 
These planets cannot appear on the Ptolemaic hypothesis, as they do on 
the Copernican, on the remote side of the sun from the earth. On the 
latter hypothesis, but not on the former, Venus should appear in quad- 
rature with the sun at maximum elongation. This fact was observed 
by Galileo with the telescope. A simple adjustment to the Ptolemaic 
system (proposed long before) made it identical with the Gopernican in 
this respect by centring the epicycles of Venus and Mercury upon the 
sun, i.e. drawing them about A. 


WITHOUT compiling any very elaborate statistics, it is apparent from 
the work of A. C. Klebs ("Incunabula Scientifica et Medica," Osiris, 
vol. IV, 1938) that the printed literature of science at the beginning of 
the sixteenth century was in the main dominated by its established 
traditions. Klebs lists more than 3,000 editions of 1,044 titles by about 
650 authors. Among these occur 95 editions (and collections) of works 
attributed to Aristotle, 18 editions of the Natural History of Pliny the 
Elder, 7 of Ptolemy's Cosmographia (but none of the Almagest), and 5 of 
Lucretius. Of ancient medical writers, Dioscorides (De materia medico) 
was printed twice, and Galen (complete so far as known) once. But 
separate works of both Hippocrates and Galen were included in num- 
erous collections of medical authorities. Celsus (De medicina) was printed 
four times. Collections of classical writers on military affairs, agricul- 
ture and astronomy were popular enough to justify more than one 
edition. Euclid was printed twice only. 

Translations from the Arabic were often printed. They include 
Avicenna's Canon of Medicine (14 editions) and the works of other great 
Islamic physicians: al-Razi (15 editions besides titles in collections), 
Mesue (19 editions) and Serapion (4 editions). Averroes* commentaries 


on Aristotle were well known in print, but not Arabic astronomical 

Works deriving from the Latin West before 1400 form a very numer- 
ous group. The long-used Etymologic of Isidore of Seville was printed 8 
times. An early product of the renaissance of learning in Europe, the 
Quastiones Naturales of Adelard of Bath, merited 2 editions. Works by, 
or attributed to, Albert the Great were immensely popular, especially 
the Secreta mulierum and the Liber aggregations, amounting to 150 edi- 
tions. Thomas Aquinas appeared in 17 editions and numerous collec- 
tions, Albert of Saxony in eleven. Two more sought-after books were 
the Sphere of Sacrobosco (3 1 editions) and the Physiognomia of Michael 
Scot (21 editions). Less well known medieval treatises, like those of 
Oresme (3), Thomas Bradwardine (3) or Walter Burley (5) all found 
publishers. The most widely read English author was undoubtedly 
Bartholomew (De proprietatibus rerum) with 1 2 editions in Latin, 8 in 
French, and others in English, Spanish and Flemish. Some medical 
writers of the middle ages were still in demand for study, to judge from 
the 31 editions of Arnald of Villanova, the 13 of Guy de Ghauliac, and 
the 9 of Mondino. The most popular of all medical treatises was still the 
Regimen sanitatis of Salerno (41 editions). With these the 35 editions of 
printed herbals before 1500 may be linked. 

The proportion of scientific books printed in the vernacular languages 
was small, but it was a microcosm of the whole. The German language 
was perhaps the best endowed in this way, and next French; in Italy, 
probably, the university tradition was too strong to render such ver- 
nacular printing profitable, and the literate class in fifteenth-century 
England did not at first demand many serious books. Many were of an 
ephemeral nature prognostications and predictions, almanacks, and 
popular treatises on the maintenance of health. This last group in- 
cludes the Livre pour garder la sante (1481), and the German Regimen 
sanitatis zu Deutsch (1472). Gaxton printed The Gouvernayle of helthe in 
1489. A book even more full of marvels than Bartholomew's, and 
equally widely available, was Mandeville's Itinerarius (in English, 
French, German, Italian and Flemish). Herbals were soon made 
accessible to the vernacular reader (German and French 1486, English 
1525), as were treatises on anatomy deriving from Mondino (German, 
Hieronymus Brunschwig, 1497; Italian and Spanish, Johannes de 
Ketham, 1493 and 1494). The Chirurgia of Guy de Chauliac was repre- 
sented in three languages before 1 500. There were also some vernacular 
books on reckoning. 

Here, then, is evidence drawn from two dissimilar sources enforcing 
the same conclusion. On the one hand, the great ItaKan printing- 
houses, supplying a highly literate and academic market, found it 
profitable to publish many of the "classics" of medieval science, often 


in several editions; on the other hand, vernacular printing shows the 
same intellectual content scaled down and vulgarized. There was no 
sudden craving for originality, no epidemic of criticism. This is also 
apparent from Mr. H. S. Bennett's study of early English publications 
dealing with science and medicine (English Books and Readers, 1475- 
1557, Ch. vi). The first surgical texts in English were based on Johannes 
de Vigo and Guy de Chauliac; the first anatomy text (by Thomas 
Vicary, 1548) on Mondino. Gaxton's Myrrour of the World (1481) 'is a 
typical example of the encyclopaedia beloved of the Middle Ages, and 
here made available to the ordinary reader with no attempt to bring 
it up to date. 5 Yet it was reprinted in 1490 and 1529. Such works, Mr. 
Bennett writes: 'contributed little or nothing that was new. Their 
compilers were content to reproduce knowledge that had been current 
for centuries, and the stationers traded in these wares confident that 
their customers would not be put off by their old-fashioned con- 
tents.' (But were the customers conscious that the contents were old- 
fashioned?) Gaxton made no greater effort to revise the geographical or 
historical knowledge which he imparted in his books, much of it taken 
directly from the thirteenth and fourteenth centuries. In short, so far 
as the respective tastes of printers, students and the general public may 
be ascertained, they were conservative; those texts which had been 
most in demand before the invention of printing were the very ones 
that became most widely disseminated after it. Printing, therefore, had 
comparatively little immediate effect on the literature of science in the 
way of substituting novelties for traditions, though it did condemn to 
darker oblivion those texts which were already half-forgotten by the 
mid-fifteenth century, and, by reason of this, it reveals the strength of 
the conservative forces extant in the early stages of the renaissance. 


STUDIES on the history of science are already so numerous that it is only possible 
in these notes to give some indications of indebtedness, and of some possible 
lines of exploration. I restrict myself here mainly to the English and French 
languages, though these are (obviously) far from containing everything of 

General: The journals his and Osiris, Annals of Science, Archives Internationales 
d*histoire des Sciences (continuing Archeion), and Revue d'histoire des Sciences, are 
indispensable. The bibliographies in Isis analyse work in the history of science 
during the last forty years; cf. also G. Sarton, A Guide to the History of Science 
(Waltham, Mass., 1952), and the handlist published by the Historical Associa- 
tion (Helps for Students of History, No. 52). The period covered by this volume is 
treated in all the general histories of science (Singer, Dampier, Wightman, 
Mason etc.) and especially by Professor H. Butterfield, The Origins of Modern 
Science (London, 1949), an< ^ H. T. Pledge, Science since 1500 (London, 1939). 
A. Wolf, History of Science, Technology and Philosophy in the Sixteenth, Seventeenth and 
Eighteenth Centuries gives many valuable scientific details but is very deficient in 


For reference and bibliography, G. Sarton, Introduction to the History of Science 
(Baltimore, 1927-48, 5 vols.) and Lynn Thorndike, History of Magic and 
Experimental Science (New York, 1923-41) are essential. There is no fully adequate 
short history for the medieval period. For Islam, cf. H. J. J. Winter, Eastern 
Science (London, 1952), A. Mieli, La Science Arabe (Leiden, 1938). Some of the 
older books, e.g. G. Singer, From Magic to Science (London, 1928) are still useful. 
A. C. Crombie, From Augustine to Galileo (London, 1952) and Robert Grosseteste 
and the Origins of Experimental Science (Oxford, 1953), takes a favourable view 
of the medieval contribution to the scientific revolution, with much biblio- 
graphical information. C. H. Haskins, The Renaissance of the Twelfth Century 
(Cambridge, Mass., 1928), and Studies in the History of Medieval Science (Cam- 
bridge, Mass., 1924) ; J. Huizinga, The Waning of the Middle Ages (London, 1924) ; 
H. Rashdali, Universities of Europe in the Middle Ages (ed. Oxford, 1936), are 
useful for background. Editions of texts are being published in quantity, e.g. 
E. A. Moody and M. Clagett, The Medieval Science of Weights (Madison, 1952); 
L. Thorndike, The Sphere of Sacrosbosco (Chicago, 1949), and The Herbal of 
Rufinus (Chicago, 1946). 


(a) There are general histories of medicine by F. H. Garrison (Philadelphia, 
1929) and A. Castiglioni (New York, 1947) the latter has the more synthetic 
treatment. A valuable survey is C. Singer, The Evolution of Anatomy (London 
1926^ J. B. de C. M. Saunders and C.D. CVMMey, Andreas Vesalius (New York, 



1950) give the anatomical illustrations with short notes. Cf. also C. Singer, 
Vesalius on the Human Brain (London, 1952) the only translation of a fair 
portion of De Fabnca; H. Gushing, A Bio-bibliography of Andreas Vesalius (New 
York, 1943); S. W. Lambert et al. 9 Three Vesalian Essays (New York, 1952); 
Saunders and O'Malley, and Singer, in Studies and Essays . . . offered to George 
Sarton (New York, 1946), articles in the Bull. Hist. Med., vol. XIV, 1943; 
J. P. McMurrich, Leonardo da Vinci the Anatomist (London, 1930), Vittorio Putti, 
Berengario da Carpi (Bologna, 1937); G. Keyncs, The Apologie and Treatise of 
Arnbroise Pare 1 (London, 1951); Sir G. Sherrington, The Endeavour of Jean Fernel 
(Cambridge, 1946). 

(b) The edition of Ptolemy which I have found most accessible is that of the 
Abbe Halma (with French translation, Paris, 1813-16), and for Copernicus the 
original printing of 1543. Secondary works are: A. Armitage, Copernicus, the 
Founder of Modern Astronomy (London, 1938), H. Dingle in The Scientific Adventure 
(London, 1952), J. L. E. Drcyer, History of Planetary Systems from Thales to Kepler 
(Cambridge, 1906), F. R. Johnson, Astronomical Thought in Renaissance England 
(Baltimore, 1937), E. Rosen, Three Copernican Treatises (New York, 1939), D. W. 
Singer, Giordano Bruno, his Life and Thought (London, 1950), D. Stimson, The 
Gradual Acceptance of the Copernican Theory (New York, 1917). 

(c) Metallurgy and industrial chemistry are dealt with in G. Agricola, De re 
metallica (trans. H. C. and L. H. Hoover, New York, 1950); C. S. Smith and 
M. Gnudi, The Pirotechnia of Vannoccio Biringuccio (New York, 1943), C. S. 
Smith and A. Sisco, Treatise on Ores and Assaying of Lazarus Packer (Chicago, 
1951). On history of pharmacology, E. Kremers and G. Urdang, History of 
Pharmacy (Philadelphia, 1940). 


There is no wholly satisfactory English work on Galileo. J. J. Fahie, Galileo, his 
Life and Works (London, 1903) is uncritical and out of date. F. Sherwood Taylor, 
Galileo and the Freedom of Thought (London, 1938) is better but limited. In trans- 
lation there are Dialogues concerning Two New Sciences (H. Crew and A. de Salvio, 
New York, 1914, 1952), Dialogues on the Two Chief Systems of the World (T. Salus- 
bury, London, 1667; S. Drake, California, 1953). Pierre Duhem's classic Etudes 
sur Leonard de Vinci (Paris, 1906-13) and Origines de la Statique (Paris, 1905-6) 
are invaluable. Cf. also L. Cooper, Aristotle, Galileo, and the Leaning Tower of 
Pisa (Ithaca, 1935), Rene Descartes, Oeuvres (ed. Ch. Adam and P. Tannery 
(Paris, 1897-1913), R. Dugas, Histoire de la Mlcanique (Neuchatel, 1950), G. 
Galilei, Opere, ed. A. Favaro (Firenze, 1890-1909), A. Koyr, Etudes GaliUennes 
(Paris, 1939; Actualit^s Scientifiques et Industrielles Nos. 852-4 most impor- 
tant), E. Mach, Science of Mechanics (Chicago, 1907), A. Maier, Die Vorlaufer 
Galileis in 14. Jahrhundert (Rome, 1949) and Die Impetustheorie (Rome, 1951), 
R. Marcolongo, "Lo sviluppo della meccanico sino ai discepoli di Galileo* * in 
Atti d. R. Ace. dei Lincei (Physical Series) vol. XIII (Rome, 1920), A. Mieli, "II 
Tricentario dei 'Discorsi e Dimostrazioni Matematiche' di Galileo Galilei" 
in Archeion, vol. XXI (Rome, 1938) critical of Duhem etc., N. 'Oresme, "Le 
Livre du Ciel et du Monde" in Medieval Studies, vols. III-V (1941-3), G. 
Sarton, "Simon Stevin of Bruges" in his. vol. XXI (1934). 



In addition to works already mentioned, A. Armitage, "The Deviation of 
Falling Bodies," Ann. Sci., vol. V (1947), I. Boulliau, Astronomia Philolaica 
(Paris, 1645), J. L. E. Dreyer, Tycho Brake (Edinburgh, i8go),Johann Kepler, 
Gesammelte Werke (Munich, 1938-), S. I. Mintz, "Galileo, Hobbes, and the 
Circle of Perfection," Isis, vol. 43 (1952), D. Shapley, "Pre-Huygenian Observa- 
tions of Saturn's Rings," Isis y vol. 40 (1949). 


The best study is H. P. Bayon, "William Harvey, Physician and Biologist," Ann. 
Sci., vols. Ill, IV (1938-9). General books are F. J. Cole, Early Theories of Sexual 
Generation (Oxford, i93o),J. Needham, History of Embryology (Cambridge, 1934), 

E. Nordenskiold, History of Biology (New York, 1946), C. Singer, History of 
Biology (New York, 1950). Cf. also H. Brown, "John Denis and Transfusion of 
Blood, Paris, 1667-8," Isis, vol. 39 (1938), L. D. Cohen, "Descartes and More 
on the Beast-Machine," Ann. Sci., vol. I (1936), C. Dobell, Antony van Leeuwen- 
hoek and his "Little Animals" (London, 1932), G. Kcynes, "The History of Blood 
Transfusion," Science News, vol. Ill (1947), A. van Leeuwenhoek, Collected 
Letters (Amsterdam, i939~),W. Pagel, "William Harvey and the Purpose of the 
Circulation," Isis, vol. 42 (1951), C. E. Raven, John Ray (Cambridge, 1950), 

F. Redi, Opere (Napoli, 1778, Milano, 1809-1 1), J. Trueta, "Michael Servetus 
and the Discovery of the lesser Circulation," Tale Jo. ofBiol. and Med., vol. XXI 
(1948), R. Willis, Works of William Harvey (London, 1847). 


There is to my knowledge no complete history of scientific method. Useful 
contemporary studies are R. B. Braithwaite, Scientific Explanation (Cambridge, 
1953), M. R. Cohen and E. Nagel, Introduction to Logic and Scientific Method 
(London, 1934), S. Toulmin, Philosophy of Science (London, 1953). Cf. also F. H. 
Anderson, Philosophy of Francis Bacon (Chicago, 1948), A. G. A. Balz, Cartesian 
Studies (New York, 1951), E. A. Burt, Metaphysical Foundations of Modern Physical 
Science (London, 1925), A. C. Crombie and H. Dingle, op. cil. for Chs. I and 
II, A. Gewirtz, "Experience and the non-mathematical in Descartes," Jo. 
Hist. Ideas, vol. II, 1941, E. Gilson, La Philosophie an Moyen Age (Paris, 1944), 
J. H. Randall, "The Development of the Scientific Method in the School of 
Padua," Jo. Hist. Ideas, vol. I (1940), B. Russell, History of Western Philosophy 
(London, 1946). 


(a) An excellent survey is M. Oinstein, The Rdle of Scientific Societies in the ijth 
Century (Chicago, 1938). Cf. also J. Bertrand, UAcadtmie des Sciences et les 
Acadtmiciens de 1666 a 7795 (Paris, 1869), T. Birch, History of the Royal Society 
(London, 1756), H. Brown, Scientific Organization in ijth Century France (Balti- 
more, 1934), A. Favaro, "Documenti per la Storia dell Accademia dei Lincei," 
Bullettino di Bibliogrqfia e di Storia delle Science, vol. XX (Rome, 1887), A. J. 
George, "The Genesis of the Academic des Sciences," Ann. Sci., vol. Ill (1938), 
F. R. Johnson, "Gresham College: Precursor of the Royal Society," Jo. Hist. 
Ideas, vol. I (1940), R. F. Jones, Ancients and Moderns (St. Louis, 1936), R. 


Lenoble, Mersenne ou la Naissance du Mtcanisme (Paris, 1943), Sir H. Lyons, The 
Royal Society (London, 1944), Notes and Records of the Royal Society, passim, 
(b) A very important essay, with full references, is M. Boas, "The Establishment 
of the Mechanical Philosophy," Isis, vol. X, 1952. Also, H. Brown, "The Utili- 
tarian Motive in the Age of Descartes," Ann. Set., vol. I (1936), R. K. Merton, 
"Science, Technology and Society in iyth Century England," Osiris, vol. IV 
(1938), G. Milhaud, Descartes Savant (Paris, 1921), J. F. Scott, The Scientific 
Work of Rene' Descartes (London, 1952), P. Mouy, La Developpement de la Physique 
CarUsienne (Paris, 1934), J. R. Partington, "Origins of the Atomic Theory," 
Ann. Set., vol. IV (1939). 


M. Cantor, Vorlesungen tiber Geschichte der Mathematik (Leipzig, 1880-1908), is 
still essential for reference. J. E. Montucla, Histoire des Mathematiques (Paris, 
1 799- 1 802) is well worth reading on the seventeenth century. Cf. also D. E. Smith, 
History of Mathematics (New York, 1923), and more popular accounts by E. T. 
Bell, A. Hooper and others. M. Daumas, Les Instruments Scientifiques aux if et 
i8 e Siecles is excellent. The only good history of a single instrument is R. S. 
Clay and T. H. Court, History of the Microscope (London, 1932). Further, I. B. 
Cohen, "Roemer and Fahrenheit," Isis, vol. 39 (1948), J. W. Olmsted, "The 
Application of Telescopes to Astronomical Instruments," Isis, vol. 40 (1949), 
L. D. Patterson, "The Royal Society's Standard Thermometer," Isis, vol. 44 
0953)5 F- Sherwood Taylor, "The Origins of the Thermometer,'Mwz. Sci., 
vol. V (1947). 


The best recent biography of Newton is that of L.T. More (London, 1934), which 
does not wholly supplant Sir D. Brewster's Memoir (Edinburgh, 1855). Other 
sources: E. N. da C. Andrade, "Robert Hooke," Proc. Royal Society A, vol. 201 
(1950), A. Armitage, " 'BorrelFs hypothesis' and the Rise of Celestial Mechan- 
ics," Ann. Set., vol. VI (1948-50), A. C. Bell, Christian Huygens and the Develop- 
ment of Science in the Seventeenth Century (London, 1947), W. J. Greenstreet (ed.), 
Isaac Newton, Memorial Volume (London, 1927), R. T. Gunther, Early Science in 
Oxford, vols. VI-VIII, X, XIII (Oxford, 1930-8), W. G. Hiscock, David 
Gregory, Isaac Newton and their Circle (Oxford, 1937), History of Science Society, 
Isaac Newton (London, 1928), A. Koyre, "La Mecanique Celeste de J. A. 
Borelli," Rev. d'Hist. des Sciences, vol. V (Paris, 1952) and "An Unpublished 
Letter of Robert Hooke to Isaac Newton," Isis, vol. 43 (1952), T. S. Kuhn, 
"Newton's *3ist Query* and the Degradation of Gold," Isis, vol. 42 (1951), 
E. F. MacPike, Correspondence and Papers of Edmond Halley (London, 1937), 
L. D. Patterson, "Hooke's Gravitation Theory and its Influence on Newton," 
Isis, vol. 40 (1949), Royal Society Newton Tercentenary Celebrations (Cambridge, 
1947), E. W. Strong, "Newton and God," Jo. Hist. Ideas, vol. XIII (1952), 
H. W. Turnbull, James Gregory Tercentenary Volume (London, 1939), A. H. 
White, Memoirs of Sir Isaac Newton's Life by William Stukeley (London, 1936). 
The best editions are those of the Principia by F. Cajori (Berkeley, 1946) and of 
the Opticks (London, 1931). The Oeuvres Completes of Christiaan Huygens (La 
Haye, 1888-1950) are invaluable for reference. 



To the books listed for Gh. V may be added: A. Arber, Herbals (Cambridge, 
1950), P. G. Fothergill, Historical Aspects of Organic Evolution (London, 1952, 
with full bibliography), Knut Hagberg, Carl Linrusus (London, 1952), W. P. 
Jones, "The Vogue of Natural History in England, 1750-70,' 'Ann. Sci., vol. II, 
1937, C. E. Raven, English Naturalists from Neckam to Ray (Cambridge, 1947), 
and Natural Religion and Christian Theology (Cambridge, 1953), C. Singer, "The 
Dawn of Microscopical Discovery," Jo. Roy. Microscopical Soc. (1915). 


There is no modern history of chemistry on the large scale. J. R. Partington, 
Short History of Chemistry (London, 1948) is an excellent introduction. Cf. also, 
on industrial chemistry, A. and N. Clow, The Chemical Revolution (London, 1952) ; 
L. J. M. Coleby, The Chemical Studies of P. J. Macquer (London, 1938), P. George 
"The Scientific Movement and the Development of Chemistry in England," 
Ann. Set., vol. VIII (1952),^ S. Kuhn, "Robert Boyle and Structural Chem- 
istry in the I7th Century," Isis, vol. 43 (1952), D. McKie, Antoine Lavoisier 
(London, 1935), and Essays of Jean Rey (London, 1951), and "Black's Chemical 
Lectures," Ann. Sci., vol. I (1936), H. Metzger, Les Doctrines Chimiques en France 
du dibul du if a la Jin du i8 e Siecle (Paris, 1923) and Newton, Stahl, Boerhaave et la 
Doctrine Chimique (Paris, 1930), L. T. More, Life and Works of Robert Boyle 
(London, 1944), J. R. Partington, "Joan Baptista van Helmont," Ann. Sci., 
vol. I (1936), and with D. McKie, "Historical Studies in the Phlogiston 
Theory," -4wi. Sci., vols. II-IV( 1937-9), T. S. Patterson, "Jean Beguin and his 
Tyrocinium Chemicum," Ann. Sci., vol. II (1937), and "John Mayow in Con- 
temporary Setting," Isis 9 vol. 15 (1931), J. M. Stillman, The Story of Early 
Chemistry (New York, 1924)^. H. White, History of the Phlogiston Theory (London, 


P. Brunet, L 9 Introduction des Theories de Newton en France au 18' Siecle (Paris, 1931), 
I. B. Cohen, Benjamin Franklin's Experiments (Cambridge, Mass., 1941 with 
useful historical introduction), E. S. Cornell, "The Radiant Heat Spectrum," 
Ann. Sci. 9 vol. Ill (1938), D. Fleming, "Latent Heat and the Invention of the 
Watt Engine," Isis, vol. 43 (1952), L. Galvani, Opere edite e inedite (Bologna, 
1841), D. McKie and N. H. de V. Heathcote, The Discovery of Specific and Latent 
Heats (London, 1935), J. C. Maxwell, Electrical Researches of Henry Cavendish 
(Cambridge, 1879), Philosophical Magazine, Natural Philosophy through the i8th 
Century (Commemoration Number, 1948), A. Volta, Collezione del Opere (Firenze, 
1816), W. Cameron Walker, "The Detection and Measurement of Electric, 
Charges in the i8th Century," Ann. Sci.,vol. I (1936), Sir E. Whittaker, History 
of Theories of Aether and Electricity, vol. I (Cambridge, 1951). 



Accademia dei Lincei, 188 
Accademia del Cimento, 151, 189- 

191, 193, 264 

Acad6mie Franchise, 188, 196 
Academic Royale des Sciences, 98, 

100, 1 86, 191, 195-8, 201, 202, 205, 

215, 333 

Berlin, 201-2 

Royal Society, 31, 99, 152-4, 182, 186, 
189, 192-5, 198, 200, 215, 216, 241, 
246, 249, 250, 266-8, 284, 289, 309, 

338, 358-9 

Aepinus, F. U. T. (1724- 1802), physicist, 

Agricola [Georg Bauer] (1490-1555), 70, 
73, 163, 221-3, 308, 321 n. 

al-Battani (d. 929), astronomer, 61, 63 

Albert of Saxony (i3i6?-9o), philo- 
sopher, 56, 81-2, 83, 85 

Albert the Great (c. 1200-80), philo- 
sopher, 28, 31, 134, 276, 278, 369 

Alchemy, 26, 69, 223-4, 244, 249, 307-8 

Aldrovandi, Ulissi (1522-1605), natural- 
ist, 156 

Alfonsine Tables, 16 

Alhazen (c. 965-1040), physicist, 21-2, 


al-Razi (d. 923-4), physician, 39, 308 

Anatomy, ancient and medieval, 3740 
and art, 41-4 
comparative, 145-6, 286 
renaissance, 41-51, 135-6, 142-4, 148 

Animalculists, 291-3 

Animism, 12, 21, 310 

Apollonius of Perga (b. c. 262 B.C.), 
mathematician, 126 

Aquinas, Thomas (12257-74), philo- 
sopher, 5 

Archimedes (287-212 B.C.), mathe- 
matician, 9, 10, 21, 76, 124, 158, 171, 

Aristotle (384-322 B.C.), philosopher, 5, 

74, 186-7,217, 339 
as biologist, 10, 28, 37-8, 71, 129, 133, 
134, 154, 156, 158, 275-7, 281-2, 
286, 289, 295, 297-8 


as physicist, 12, 19, 21, 23-6, 35, 53, 
56, 66 ff., 76, 78, 92, 97, 100, 103, 
106, 109 ff., 114, 117, 165, 172,206- 
207, 210, 260-1, 306, 313 
scientific method of, 160-3, J 68-9, 185 
Arzachel (c. 1029-87), astronomer, 61 
Astrolabe, 4, n, 14, 17, 235 
Astronomy, Copernican, 3, 51-68, 108, 
119, 192, 194, 261, 370-1 ; and re- 
ligion, IO2-6 
Galilean, 107-16 
Kepler's Laws, 117, 121-6, 248, 260, 


Newton and, 248 

Ptolemaic, 3, 11-18, 52-65; con- 
stants of, 15 n. 

Atomism, see Philosophy, mechanical 
Averroes (b. 1126), philosopher, 138 
Avicenna (979- IO 37) physician, 4, 39, 

71, 138, 140 

Avogadro, Amadeo (1776-1856), physi- 
cist, 338 

BACON, FRANCIS (1561-1626), philo- 
sopher, 7, 31, 34, 75 n., 135, 182, 

189, 192-4, 197, 201-2, 2O7, 211, 
213, 219, 235, 243 

on scientific method, 161, 164-9, 

173-4, 1 80, 183-5 
Bacon, Roger (1214-94), philosopher, 

6, 22, 31, 34, 163, 306, 309 
Baer, K. E. von (1792-1876), biologist, 

Baker, Henry (i 69$- 17 74), microscopist, 


Ballistics, 78, 93, 190, 230 
Banks, Sir Joseph (1743-1820), natural- 
ist, 191, 280, 290, 339 
Barrow, Isaac (1630-77), mathematician, 

231, 247, 249 
Bartholomew the Englishman (/. c. 

1220-40), 30, 72, 278 
Basil Valentine, pseudonym, 69, 224 
Bauhin, Caspar (1560-1624), botanist, 

131, 283 
Bausch, Lorentz, 201 

I 25 


Bayle, Pierre (1647-96), writer, 204 

Beccaria, G. B., 333 

Becher, J. J. (1635-82), philosopher, 326 

Beddoes, Thomas (1760-1808), physi- 
cian, 325 

Beeckman, Isaac (1588-1637), philo- 
sopher, 89-92, 93, 96, 100, 207 

Beguin, Jean (c. 1550-1620), chemist, 
312, 317 n. 

Benedetti, Giovanbattista (1530-90), 
mathematician, 78, 87 

Bennet, Abraham (i75~99)> 35 2 

Bentley, Richard (1662-1742), philo- 
sopher, 272 

Berengario da Carpi (1470-1550), ana- 
tomist, 38, 41, 44, 45, 138 

Berkeley, George (1685-1735), philo- 
sopher, 185 

Berzelius, J. J. (1779-1848), chemist, 362 

Bewick, Thomas (1753-1828), engraver, 

Biological Illustration, 29-30, 41 ff,, 48, 

71, 277, 278-9, 369 
Biological Sciences : 

blood transfusion, 153-4 

Cartesian ideas on, 14851 

circulation of the blood, 141-8 

evolution, 284, 296-8 

medieval ideas, 27-31 

microscopy, 240-2, 286-7, 290 flf. 

physiology, 135-41, 152-3, 287-9, 291 

renaissance of, 130-4, 275-84 

taxonomy, 276, 281-6, 290, 294-6 
Biringuccio, Vanoccio (Jl. c. 1540), 

metallurgist, 70, 221-2 
Black, Joseph (1728-99), chemist, 82 n., 

224, 308, 318, 328, 329-30, 332-4, 

337 ; on heat, 344-7 
Boccaccio, Giovan (1315-75), 8 
Bode, J. E. (1747-1826), astronomer, 126 
Boerhaave, Herman (1668-1738), chem- 
ist, 291, 295, 318, 328 
Bonamico, 78 

Bonnet, Charles ( 1 720-93), naturalist, 241 
Borelli, Alfonso (1608-79), 77, 150, 247, 

and theory of gravitation, 264-6, 267 
Boswell, Sir William (d. 1649), diplomat, 


Boyle, Robert (1627-91), philosopher, 
23 n., 25, 105, 143, 151, 172, 182, 
191-6, 208, 216, 219, 220, 223, 225- 
226, 238, 291, 343, 365 

and chemistry, 304-5, 309, 311, 313, 

316-28, 333, 337, 338 
and mechanical philosophy, 211-13, 


and Newton, 244, 247, 272 n. 
Boyle's Law, 227 
Bradley, James (1692-1762), astronomer, 


Brahe, Tycho, see Tycho 

Briggs, Henry (1556-1630), mathe- 
matician, 229 

Brouncker, William, Viscount (1620?- 
1684), P.R.S., 193 n., 194 

Brunfels, Otto (1489-1534), herbalist, 
131, 278-9, 369 

Bruno, Giordano (1548-1600), philo- 
sopher, 55, 74, 77, 103-5 

Brunschwig, Hieronymus (c. 1450-1512), 

Buffon (George Louis Leclerc, Comte de, 
1707-88), 297-8 

Buridan, Jean (c. 1295-1358), philo- 
sopher, 6, 20-21, 56 

Burnet, Thomas (1635-1714), divine, 

CAIUS, JOHN (1510-73), physician, 38 

Calendar, 3, 16, 53 

Caloric, 328, 343-6 

Camerarius, Rudolph Jacob (1665 
1721), botanist, 157, 294 

Canano, Giovanbattista, of Ferrara 
(1515-79), anatomist, 41, 46 

Cardano, Jerome (150176), philosopher, 
20, 78, 156, 163, 226 

Carlisle, Sir Anthony (1768-1840), sur- 
geon, 360 

Carnot, Sadi (1796-1832), engineer, 347 

Cassini, Jacques (1677-1756), astrono- 
mer, 341 

Cassini, Jean (1625-1712), astronomer, 

Cavalieri, Bonaventura (1598-1647), 
mathematician, 226, 227, 231 

Cavendish, Sir Charles (1591-1654), 
mathematician, 192 

Cavendish, Henry (1731-1810), on 
chemistry, 318, 328-32, 334 n., 335 
on physics, 272, 353-5 

Celsus (fi. c. A.D. 14-27), physician, 41 

Cesalpino, Andreas (1519-1603), botan- 
ist, 131, 279, 283, 321 n. 



Cesi, Frederigo, Duke of Aquasparta, 188 
Charles II, K. of England (1660-85), 


Chaucer, Geoffrey (1340?-! 400), 4 
Chemistry, 24-6, 131, 212, 244, 249, 

303-3 8 

electrochemistry, 360-3 
iatrochemistry, 309-13, 317-18 
industrial, 70, 201, 220-4, 304, 306-7 

Christian IV, K. of Denmark (1588- 
1648), 118 

Clairaut, Alexis Claude (1713-65), 
mathematician, 340, 341-2 

Clement VII, Pope (1523-34), 54 

Colbert, Jean Baptiste (1619-83), 195, 


Collingwood, R. G., 9 
Colombo, Realdo (1516-59), anatomist, 

46, 48, 142 

Combustion, 324-5, 327, 330, 332-6 
Comenius,J. A. (1592-1671), 194 n. 
Copernicus, Nicholas (1473-1543), as- 
tronomer, 6, 1 6, 35, 74, 102, 108-9, 
114-17, 120 ff., 163-4, 174*234,261, 
263, 275 

compared with Vesalius, 36-7 

system of, 51-68 
Cordus, Valerius (1515-44), botanist, 

Coulomb, Charles Augustin (1736- 

1806), engineer, 352-4 
Cullcn, William (1710-90), physician, 

Cuvier, Georges (1769-1832), naturalist, 

297, 30i 

D'ALEMBERT (Jean le Rond, 1717-83), 
mathematician, 340 

Dalton, John (1766-1844), chemist, 215, 

Dante Alighieri (1265-1321), 72 

Darwin, Charles (1809-82), biologist, 
256, 275, 296-8, 301, 341 

Davy, Sir Humphry (1778-1829), chem- 
ist, 325, 360-2 

Dee, John (1527-1608), mathematician, 

55> 72 
De Graaf, Regnier (1641-73), biologist, 


De Groot, 100 
De 1'ficluse, Charles (1524/5-1609), 

botanist, 279 

De rObel, Matthias (1538-1616), natu- 
ralist, 283 

Democritus (c. 460-370 B.C.), 97, 103, 

Desaguliers, John Theophilus (1683 
1744), physicist, 340 

Desargues, Gerard (1593-1662), mathe- 
matician, 191 

Descartes, Ren6 (1596-1650), 83 n., 89 
92, 93~4, 99. ioo, 105-6, 113, 127, 
191, 196, 198-200, 205, 215, 236, 
and biology, 129, 138, 298 
ideas of matter and motion, 95, 207- 


and mathematics, 227, 228, 230 
mechanics of, 96-8 
and Newton, 99, 244, 247, 270-1 
and optics, 251, 252 ., 254 
physiological ideas of, 148-52, 157 
on scientific method, 164, 177-84 
and theory of gravitation, 260, 264-5 

De Thou, J. A. (1553-^ 17)1 *95 

Diderot, Denis (1712-84), philosopher, 


Digges, Thomas (d. 1595), mathemati- 
cian, 104 

Dioscorides (Jl. c. A.D. 50), herbalist, 10, 
217, 276, 277, 279, 281 

Doliond, John (1706-61), optician, 242, 


Dorninico Soto (1494-1570), theologian, 
83-5, 88, 91-2 

Drebbel, Cornelius (1572-1634), 192 

Drury, John, 1 93 n. 

Dryander, Johann (c. 1500-60), physi- 
cian, 41, 46 

Dufay, Charles (1698-1739), electrician 
349-50, 362 

Dumas, J. B. A. (1800-84), chemist, 292 

Dupuy, 195 

Dttrer, Albrecht (1471-1528), 278 

Dymock, Cressy, 193 n. 

ELEMENTS, 313-15, 320-3 

Aristotelean, 1 7 ff., 23-6, 60, 208 

Elizabeth I, Qu. of England (1558- 
1603), 72 

Ellis, John (17107-76), naturalist, 241, 

Ent, Sir George (1604-89), physician, 




Epicurus (340-270 B.C.), 97, 187, 207 

Ercker, Lazarus (?~I593), metallurgist, 

Estienne, Charles (1504-64), anatomist, 
41,44,46, 139 

Euclid (fl. c. 300 B.C.), 10, 171 

Eugene, Prince of Savoy (1663-1736), 

Euler, Leonhard (1707-83), mathe- 
matician, 342-3 

Eustachio, Bartolomeo (1520-74), ana- 
tomist, 46 

Evelyn, John (1620-1706), virtuoso, 
i93/*- i94>200 

Experimental method, 6, 32-3, 45, 86, 
99* 129-35, 145-6, 173-6, 181-3, 185, 
189-91, 199, 216, 223-4, 233, 255- 
257, 270, 273-4 

Aquapendente (1537-1619), physician, 
139, 286, 298 
Fabricius, Johann (fl. c. 1605-15), 

astronomer, 108 

Fabroni, Giovanni (1752-1822), 360 
Fahrenheit, Gabriel Daniel (1686-1736), 

physicist, 238, 341, 344 
Fallopio, Gabriele (1523-62), anatomist, 


Faraday, Michael (1791-1867), physi- 
cist, 185, 332, 353, 362 
Ferdinand II, Duke of Florence, 190 
Fermat, Pierre ( 1 60 1 -65) , mathematician, 

94, 191, 230, 231, 252 n. 
Fernel, Jean (1497-1558), physician, 46, 

135-6, 138 

Field, John (i 5257-87), astronomer, 55 
Mamsteed, John (1646-1719), astrono- 
mer royal, 120, 198-9, 238 
Foster, Samuel (c. 1600-52), astronomer, 

Franklin, Benjamin (1706-90), 347, 

35<>-3> 358> 362 
Frederick I, Elector of Brandenburg and 

K. of Prussia (1688, 1700-13), 201 
Frederick II, Emperor (1194-1250), 28 
Freind, John (1675-1728), physician, 

Fresnel, Augustin (1788-1827), engineer, 


Fuchs, Leonard (1501-66), herbalist, 
131* 278-9, 280, 369 

GALEN (A.D. 129-99), physician, 9, 10, 

36> 37-5', 7i, 74, '29, i3i-6> 138, 141* 
152, 217, 310, 313 

Galileo Galilei (1564-1642), 18, 35, 45, 
48, 56-7. 59, 65, 68, 98-100, 105, 
106, 127, 135, 147-8, 158, 167, 182, 
188-90, 194-5, '99, 207,211,217, 
219, 225-6, 230, 233-5, 238, 275, 

30i, 33', 335, 337, 365-6 
on astronomy, 107-17, 120 n., 121 
and Descartes, 92-101 
importance of, 74-7 
on mechanics, 78-92 
and Newton, 247 n., 261, 263, 270, 


scientific method of, 164, 168-78, 
180-1, 183-4 

Galvani, Luigi (1737-98), anatomist, 
355-8* 362 

Gassendi, Pierre (1592-1655), philo- 
sopher, 156, 157, 191, 196, 207-8, 215 

Geber, pseudonym, 69, 306 

Gemma Frisius (1508-55), astronomer, 


Generation, 25, 27-8, 284, 290-3, 297 
spontaneous, 28, 154-7, 284, 291 

Geoffroy, Etienne Francois (1672-1731), 
chemist, 326 

Gerard of Cremona (c. 1114-87), trans- 
lator, 4, 39 

Gesner, Conrad (1516-65), naturalist, 
279, 282-3, 298 

Gibbon, Edward (1737-94), historian, 


Giese, Tiedeman, 55 
Gilbert, William (1540-1603), physician, 
72, 86, 89, 93, 96, 185, 188, 192, 211, 

235, 348 

and gravitation, 260-2, 263 
Glauber, Rudolph (1604-70), chemist, 

133* 3"* 317 
Glisson, Francis (1597-1677), physician, 

Goddard, Jonathan ( 1 6 1 7-75) , physician, 

Graunt, John (1620-74), statistician, 225 

Gravitation, theory of, 66, 79, 86, 99, 

126-8, 206, 248, 259-74, 342 
action at a distance, 96, 99, 127, 260, 

265, 272 

Gray, Stephen (d. 1736), electrician, 349 
Gregory, James (1638-75), mathemati- 
cian, 239 



Grcsham, Sir Thomas (i5i9?~79), mer- 
chant, 187 n. 

Gresham College, 187 n., 192, 205 

Grew, Nehemiah (1641-1712), botanist, 
157, 240, 284, 288-9 

Grimaldi, Francesco Maria (1613-63), 


Grosseteste, Robert (d. 1253), bishop of 
Lincoln, 5-6, 22 

Guericke, Otto von (1602-86), 348 

Guido da Vigevano (c. 12801350), 
physician, 7 

Giinther, Johann (1487-1574), anatom- 
ist, 44, 45, 138, 140 

Guy de Chauliac (d. 1368), surgeon, 71 

HAAK, THEODORE (1605-90), translator, 


Hales, Stephen (1679-1761), physio- 
logist, 287, 291, 329 

Haller, Albrecht von (170877), physio- 
logist, 301 

Halley, Edmond (1656-1742), astrono- 
mer, 120, 199, 246, 249, 268, 269 

Harriot, Thomas (1560-1621), mathe- 
matician, 192, 230 

Harrison, John (1693-1776), horologist, 

Hartlib, Samuel (d. 1670?), 193, 194 n. 

Hartsoeker, Nicholas ( 1 656-1 725) , micro- 
scopist, 292 

Harvey, William (1578-1657), physician, 
10,37,46,51, H9, 15^2, 158, 185, 
192, 235, 239, 286, 298 
on generation, 154-7, 291, 292 
on the circulation, 1 34-48 
predecessors of, 139-43 

Hawksbee, Francis (d. 1713?), electrician, 

340, 348 

Heisenberg, Werner, 114 
Helmont, Johann Baptista van (1577 or 

1580-1648), philosopher, 312-17, 319, 

320; 324 
Henri de Mondeville (fl. c. 1280-1325), 

surgeon, 40 
Heraclides of Pontus (c. 388-310 B.C.), 

astronomer, 65 n. 
Herbals, 29, 71, 131, 276-82 
Hero of Alexandria (ist cent. A.D.), 

mechanician, 10, 207 
Herschel, Sir William (1738-1822), 

astronomer, 242, 258 n. 

Hevelius, Johann (1611-87), astronomer, 
120, 236, 240 

Hipparchus (fl. c. 161-127 B.C.), as- 
tronomer, 15, 61, 118 

Hippocrates (c. 460-380 B.C.), physician, 


Hobbes, Thomas (1588-1679), philo- 
sopher, 104, 192 

Hoffman, Friedrich (1660-1742), chem- 
ist, 291 

Hooke, Robert (1635-1703), physicist, 
119 n., 152, 194, 199, 211, 219, 240, 
246, 286, 296 ., 298, 324-5, 343 
on gravitation, 260, 264-9, 271 n. 
on optics, 251-5 

Horrocks, Jeremiah (1617-41), as- 
tronomer, 192 

Humanistic scholarship, 1-2, 8-10, 53, 
188, 229, 279, 371-3 

Hume, David (1711-76), philosopher, 


Hunter, John (1728-93), anatomist, 301 
Hus, John (c. 1370-1415), 2 
Huygcns, Christiaan (1629-95), physi- 
cist, 98-9, 181-2, 190, 194 n., 195-7, 
203, 232-3, 271 

and gravitation, 267-8, 273 

and Newton, 250 n. 

and optics, 252 ., 255, 259 
Huygens, Constantyn, 250 n. 

IBN AL-NAFIS AL-QURASHI (c. 1208-88), 

physician, 140 

Instrument-making and Instruments, 69, 
119-20, 234 ff. 

air-pump, 2367 

balance, 224, 235 

barometer, 190, 238 

electrical, 348-9, 352-3, 359 

hygrometer, 190 

microscope, 235-6, 239-41 

telescope, 107, 235, 239-40, 242, 248 

thermometer, 190, 238 
Inventions, I, 6-7, 22, 99 
Isidore, Bp. of Seville (c. 560-636), 278 
Islamic Science, 3, 4, u, 17, 21-2, 39, 

53, 5 6 > 61, 69 n., 118, 138, 140, 163 n., 

220, 229, 230, 306-8 

JABIR IBN HAYYA"N (fl. c. 775), physician, 



James I, K. of England (1603-25), 192 
James II, K. of England (1685-8), 249 
John of Holywood (Sacrobosco) (c. 

1200-50), 12 
John Stephen of Calcar (b. 1499 ; d. 

1546-50), artist, 48 

Johnson, Samuel (1709-84), 293, 339 
Johnson, Thomas (d. 1644), botanist, 156 
Jordanus Nemorarius (?/. c. 1 180-1237), 

mechanician, 6 

Joule, James Prescott (1818-89), physi- 
cist, 256, 346 
Journals, scientific, 203-4 
Jung, Joachim (1587-1657), botanist, 284 
Junker, Gottlob Johann (1680-1759), 
physician, 326 n. 

KEILL, JOHN (1671-1721), mathemati- 
cian, 326 

Kepler, Johann (1571-1630), astrono- 
mer, 48, 68, 1 06, 108-9, *7'> l8 5> 
192 n., 226, 231, 243, 247, 260 
astronomical discoveries of, 1 16-28 
and gravitation, 261-5, 267 

LAGRANGE, JOSEPH Louis (1736-1813), 

mathematician, 340 
Laplace, Pierre Simon Marquis de ( 1 749- 

1827), mathematician, 274, 334, 340, 


Lavoisier, Antoine Laurent (1743-94), 
chemist, 24, 224, 256, 293, 301 

and chemistry, 303, 305, 308, 316, 322, 
324-5, 328, 329, 331, 332-8 

and physics, 345-7 
Laws of Nature, 171-3 

Acceleration, 80, 92-4, 1 1 3 

Inertia, 86-7, 89, 92-3, 96 
Leeuwenhoek, Antoni van (1632-1723), 

microscopist, 131, 203, 236, 241-2, 

275, 286, 290, 292, 298 
Leibniz, Gottfried Wilhelm (1646-1716), 
201-2, 204,216, 273, 297 

and mathematics, 227, 231-2, 250 n. 
Lemery, Nicholas (16451715), chemist, 


Leonardo da Vinci (1452-1519), 9, 10, 
20, 29, 41-2, 46, 78-9, 82, 91, 138, 163, 


Libavius, Andreas (i54O?-i6i6), iatro- 
chemist, 311-13, 317 

Linnaeus, Carl (1707-78), naturalist, 

131, 275, 282, 283, 285, 290, 293-6, 

298, 341 
Locke, John (1632-1704), philosopher, 

250, 274 
Logarithms, 229 
Longomontanus, Christian (1562-1647), 

astronomer, 123 
Louis XIV, fC. of France (1660-1715), 

Lower, Richard (1631-91), physician, 


Lucretius (c. 98-55 B.C.), poet, 9, 103, 

Lull, Raymond (1232-1315/16), philo- 
sopher, 224 

Lusitanus, Amatus (1511-68), anatomist, 

Luther, Martin (1483- 1546), reformer, 55 

MAGH, ERNST (1838-1916), physicist, 86 
Machiavelli, Niccolo (1469-1527), 9 
Maclaurin, Colin (1698-1746), mathe- 
matician, 342 
Macquer, Pierre Joseph (1718-84), 

chemist, 308 

Macrobius (fl. c. 400), commentator, 4 
Malpighi, Marcello (1628-94), biologist, 
146, 156-7, 240, 242, 275, 286-8, 
290-1 ; 293 

Marco Polo (c. 1250-1323), i 
Marcus Graecus (prob. pseudonym, c. 

1300), 306 

Margarita Philosophica^ 1 1 ff., 20, 22-3, 26 
Martianus Capella (fl. c. 470), Roman 

writer, 65 
Massa, Niccolo (d. 1569), anatomist, 41 


vxMathematics, 9, n, 69, 97, 100, 126, 
170-1, 178, 1 80, 192, 218, 224-34, 2 48 

Mattiolo, Pietro Andrea (1500-77), 
herbalist, 279 

Maupertuis, P. L. Moreau de (1698- 
1759), mathematician, 341 

Maxwell, James Clerk (1831-79), physi- 
cist, 265 n. 

Mayer, Robert (1814-87), physician, 346 

Mayerne, Sir Theodore Turquet de 
(1573-1655), physician, 311 n. 

Mayow, John (1645-79), physician, 325, 

Mazarin, Jules Cardinal ( 1 602-6 1 ) , 1 96 



Medicine, 3-4, u, 37-51, 70-1, 73, 

130-4, 200, 277-81, 310 ff. 
Mendel, Gregor (1822-84), botanist, 

130, 275 

Merrett, Christopher (1614-95), physi- 
cian, 193 
Mersenne, Marin (1588-1648), 94, 113, 

191, 195, 196, 199 
Michelangelo (1475-1564), 41 
Michieli, 280 

Milton, John (1608-74), 193 n., 197 n. 
Mondino dei Luzzi (c. 1275-1326), 

anatomist, 40, 45 
Montmor, Habert de, virtuoso, 194 ., 

196, 200 
Moray, Sir Robert (d. 1673), virtuoso, 

193 n., 194 

More, Henry (1614-87), theologian, 247 
Moufet, Thomas (1533-1604), physician, 

156, 282 
Musschenbroek, Pieter van (1692-1761), 

physicist, 340 

NAPIER, JOHN (1550-1617), mathe- 
matician, 192, 228-9 
Natural History (see also Biology), 10, 25, 
27-31, 71, 130, 198, 274 ff., 298-302 
Navigation, 3, 6, 192, 219, 235 
Neckham, Alexander (1157-1217), philo- 
sopher, 31 
Needham, John Turberville (1713-81), 


Needham, Joseph, 77 n. 

Newton, Sir Isaac (1642-1727), 21, 88, 

94, 102, 105, 116, 171-3, 177, 182, 

198-9, 205, 216, 223, 226, 234, 275, 

294, 321, 326, 331-2, 337, 340-1, 

354, 3^3, 365 
and Descartes, 99, 2 1 1 
and gravitation, 263-70 
life etc., 244-50 
alid mathematics, 229, 231-3 
mechanical philosophy of, 213-15, 


and optics, 239, 250-1, 254-9, 342-3 
Nicholas of Cusa (1401-64), philosopher, 

ii, 59, 104, 313 

Nicholas of Damascus (c. 64-1 B.C.), 276 n. 
Nicholson, William (1753-1815), 360 
Nollet, ;4M/Jean-Antoine (i 700-70), 354 
Novara, Domenico Maria da (1454- 

1504), astronomer, 54 

OBSERVATION, accuracy of, 17, 43, 49, 
52-3, 1 15, 1 18-19, 167, 199, 217, 223-4, 

Oersted, Hans Christian (1777-1851), 

physicist, 362 
Oldenburg, Henry (i6i5?~77), publicist, 

191, 193 > 194 > 1 9$> 203, 249 
Omar Khayyam (c. 1040-1124), mathe- 
matician, 230 

Oresme, Nicole (c. 1323-82), philosopher, 
6, 20-i, 24, 53, 78, 85, 87, 103, 365 
on diurnal rotation, 5660 
variation of qualities, 80-3, 88 rc., 89, 

Osiander, Andreas (1498-1552), divine, 

Ovists, 291-3 

PALEY, WILLIAM ( 1 743-1 805) , theologian, 

Paracelsus (Theophrastus Bombastus von 
Hohenheim (c. 1493-1541), 70, 73-4, 
132-3, 224, 304, 308-12, 218 

Pare, Ambroise (1510-90), surgeon, 71, 

Pascal, Blaise (1623-62), mathematician, 

100, 101, 190-1, 195, 227 
Pasteur, Louis (1822-95), bacteriologist, 

154, 256, 291 

Paul III, Pope (1534-49), 55 
Peiresc, Fabri de (1580-1637), virtuoso, 

Pell, John (161185), mathematician, 

Penny, Thomas (c. 1530-88), botanist, 

282 n. 

Peter of St. Orner (c. 1350-1400), 307 
Peter the Stranger (fl. c. 1270), physicist, 


Petrarch, Francesco (1304-74), poet, 8 
Petty, Sir William (1623-87), political 

economist, 193 n., 194 n. y 225-6 
Peurbach, Georg (1423-61), astronomer, 


Philosophy, mechanical, 9-10, 21, 97, 
101, 148-51, 157, *59, 205-16, 248, 
254, 259-60, 271, 274, 289 
and chemistry, 319-26 
Philosophy of science, Baconian, 164-8, 


Cartesian, 177-84 
Galilean, 168-77 



Philosophy of science, in Greece, 1 59-63 

Newtonian, 255-8, 270-4 
Phlogiston, 326-36 
Physical sciences : 
Acoustics, 23, 226 
Dynamics, Aristotelean, 18 ff., 52-3, 

57, 66-8 

Galilean, 78-92, 110-14, 11 7 
Impetus theory, 1921, 56, 7887 
Electricity, 206 ; static, 347~55 J 

current, 355-63 
Heat, 23-4, 169-70, 190, 206, 328, 

Optics, 21-3, 180, 209-10, 214, 235-6, 

239, 245, 248, 250-9, 342-3 
Magnetism, 206, 210 
Mechanics, Newtonian, 245, 248, 

262-74, 34^-2 
Statics, 21, loo-ioi 
Picard, Jean (1620-83), astronomer, 198, 


Plantades, 292 

Plato (429-348 B.C.), 4, 20, 24, 162, 306 
Plattes, Gabriel (fl. c. 1640), agronomist, 

Pliny the Elder (A.D. 23-79), 4 7 J > 2I 7> 

276, 298, 306 
Poisson, Sime'on Denis (1781-1840), 

physicist, 354 

Pole, Reginald, Cardinal (1500-58), 41 
Pope, Alexander (1688-1744), poet, 250 
Porta, Giovanbaptista (c. 1550-1615), 

1 88 

Power, Henry (1623-68), physician, 291 
Prevost, J. L., 292 

Priestley, Joseph (1733-1804), on chem- 
istry, 328 ff. 

on physics, 339, 352-3 
Proust, Marcel (1871-1922), writer, 299 
Ptolemy (fl. A.D. 127-51), astronomer, 12, 

15-17, 21, 52 ff., 61, 63 ff., 107, 109, 

117, 162 

Pythagoras (?58o-?5OO B.C.), mathe- 
matician, 63 

RANELAGH, Countess of, 193 n. 
Raphael Sanzio (1483-1520), artist, 41 
Ray, John (1627-1705), naturalist, 131, 

I57> 197 n., 275, 281, 284-5, 288, 294, 

296, 297 
R6aumur, Re"ne Antoine Ferchault de 

(1683-1757), 241,290, 341 

Recorde, Robert (i5io?-58), mathe- 
matician, 55 

Redi, Francesco (1626-98), physician, 
130, 156-8,284,298 

Regiomontanus (Johann Miiller, 1436- 
1476), astronomer, n, 53 

Reinhold , Erasmus (151153)) astrono- 
mer, 54-5, 58 

Reisch, Gregor (d. 1525), see Margarita 

Renaissance, 6-10, 29-30 

Renaudot, Th6ophraste (1583-1653), 
journalist, 195 

Rey, Jean (b. c. 1582, d. after 1645), 
physician, 324